Speaking only on the watercolor side of things!
Paper can be very subjective... but this is my absolute favorite. It's a bit pricey. However, this paper hardly buckles at all when I use it and it dries completely flat - Arches and all the other popular ones usually require me to iron the paper after, and I've really just stopped using anything else. It also takes a lot of abuse. The pads are good, but there are also large sheets you can cut down to whatever size you like.
https://www.dickblick.com/products/laquarelle-canson-heritage-watercolor-pads/ (You can checkout with Amazon using Dicks and their prices are often much better)
Here are some brushes I've picked up that I really like.
https://www.amazon.com/gp/product/B007PMP5DS/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 This one is great for details, and I prefer it greatly over typical script liners
https://www.amazon.com/gp/product/B00512C1VS/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 Just an overall great brush. It's really floppy so takes some getting used to if you haven't used one like it before.
https://www.amazon.com/gp/product/B004BNCNCK/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 Similar to the first brush I listed. Great for tree branches etc
https://www.amazon.com/gp/product/B000H86SUQ/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 Just some cheapy hake brushes. I These are super duper soft and great for laying down washes.
And with all those brushes... https://www.amazon.com/gp/product/B0027AEANE/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 (it's like .40 cent cheaper on Dicks)
And just some other random things I have bought in the past two years that I absolutely love/would buy again
https://www.dickblick.com/products/gatorfoam-board/ These are great to tape or stable to, and last MUCH longer than Masonite boards
https://www.amazon.com/gp/product/B000WS3CC8/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 I hate how plastic palettes make the paint bead up. Porcelain doesn't allow that to happen and doesn't stain. I love this little tray, need to get more.
https://www.dickblick.com/products/escoda-perla-toray-white-synthetic-round/ These are really nice brushes
https://www.dickblick.com/products/grumbacher-goldenedge-round/ As are these
https://www.amazon.com/gp/product/B0077RHJSK/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 These are great white pens to add details after paint has dried
This https://www.amazon.com/gp/product/B004XL1D26/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 + https://www.amazon.com/gp/product/B00ELGCSU4/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 this is the best method for applying masking fluid i've found (preserving the white of the paper)
I've done business with Plaza Japan in the past, they have a good selection and low prices; you'll pay for shipping so best or order more than just one product to take advantage of that.
Amazon isn't bad, just check the prices compared to other stores. I've gotten great deals, and I've seen items posted at silly prices too. If you got prime then shipping is covered, although keep in mind that lots of the low price ship kits are shipped from Japan so the free shipping takes a while. Also read the reviews, I've had a couple of sellers not ship but Amazon had my back every time.
As for tips for a beginner, get the right tools right off the bat, this tool kit is a good start, I like these brushes (although you might want to get an additional bigger one as well), and I use this brush cleaner. Get a paint pallet for mixing, remember some paints like Tamiya need thinner while ones like AK don't. For more on brushes watch this quick video. You'll likely want some modeling masking tape. If you'll be doing something with lots of decals like a Carrier get some Microset & Microsol plus decal/hobby scissors. You'll need some kind of filler putty, I like miliput. Later on you'll want to mess with things like washes (vallejo makes a great out of the bottle wash) simple washes can make you stuff suddenly look pro because of what it does to small details, if you're going to be doing ships with specific paint schemes look in to the AK sets they'll be 5-6 colors all as part of a theme (like Royal Navy ships).
Most importantly you should start with something cheap. Your first few models will be learning experiences, so play around with those cheap $10 IJN destroyer kits till you get comfortable, use it to test painting techniques, then build that $50 HMS Ark Royal kit.
I agree with brushes not lasting forever and such but get this stuff as well.
It will help them last a little bit longer.
Some nice starter brushes
Wet palette (helps keep paint from drying out while painting)
Learn-to-paint kits with paint, brushes, miniatures and tutorial guide
Hobby knife for scraping excess material from miniatures
Clippers for cutting miniatures off of sprues
Brush soap for cleaning brushes
I don't know what your family does or doesn't have, but these are the things I would have wanted when I first started.
She did just start painting miniatures, but I'm not sure what would be a good gift for that.
Ooooh I love mini painting. What are the useful tools and resources, hmmm.
For army painting I'd say an airbrush compressor with a tank, with an the acompanying cheap gravity-fed dual action airbrush with a .5mm nozel to start. If you look em up on amazon, 'air brush tank' you'll see a tonne of sets all looking the same (they are, just with different airbrush) for around $150. Depends what you mean by 'just started' though, I wouldn't dive in to this on week 1. 6 months in maybe.
For painting normally, and for someone who just started what are the 'game changing' items. Ok so: - Wet pallete, such as the one from army painter. It keeps your paints fresh and moist and easy to work with for ages $25 or #35 with more refills. I'd go the $35
You want your brushes to last ages right, well that's why we use brush soap. Treating your brushes with [master's brush soap for ($10)[https://www.amazon.com/General-Pencil-105-BP-Masters-Preserver/dp/B0027AEANE/ref=sr_1_2?keywords=master%27s+brush+soap&qid=1636524979&qsid=139-0808896-2360434&sr=82&sres=B0027AEANE%2CB0049UZ8Z4%2CB001TNR7VM%2CB00F38YVQS%2CB009OP2M1M%2CB001E22PME%2CB004BPPL40%2CB085HHBP5C%2CB0009RRT9Y%2CB01GR2LOYU%2CB07L2QJPVJ%2CB08RNBRQYM%2CB075L8LCTG%2CB0027A79I2%2CB01BSB56OY%2CB000CC91GK%2CB00178WGHY%2CB01MS41HK6%2CB087RH77GX%2CB0028FQ0TK] as seen in this vid: https://www.youtube.com/watch?v=GeDwTY7C9xs
This brush cleaner meanwhile: https://www.thesydneyartstore.com.au/product-group/1379-incredible-brush-cleaner-250ml/category/125-cleaners is how you get into her good books after she spills paint on some clothes, which will happen. A couple of drops of this, rub it in, a couple more, rub it in, a couple more, into the washing machine, then the dryer if ya have one. This will remove 90% of it in one cycle. 10US. It can also help rescue really far gone natural hair brushes, but it's 50/50 chance. If you get to this point, it's likely already dead.
A painting handle also really helps, makes minis easier to hold with the balance being in the wrist and forearm, not the finger which makes your hands sooooo much steadier. Well worth it.
Anything else they try to sell ya is unncessary imo. Eventually you might want a lightbox, and a good natural light. But those are down the line, no other accessories needed.
I'm assuming the basic gear, snips, glue, mouldline scraping tool...