Awww, this is so sweet! Nail art doesn't have to be expensive at all, the salon I go to uses a lot of toothpicks and tiny brushes for most of their fancy stuff. The problem is with actually DOING the art. It takes a super steady hand and some serious talent. I'm awful at it which is why I have them done instead. Have you considered getting her a gift card to a salon? If you go that route, make sure to show them some pictures of what you have in mind and ask if they can do it. If they're legit they'll have some pictures or samples to show you.
As far as kits go, $20 on amazon should be just fine. I would recommend getting one with the little bottles, because the little bottles come with little brushes (which is essential for doing art). Maybe some extra tiny brushes for detail. Also dotting pens are a fancy and durable alternative to toothpicks. If she's into bling, nail jewels are cool and fancy as fuck. Lastly (and very important), invest in some serious base coat and top coat. There's nothing worse than spending an hour getting your nails did just to have them chip an hour later. OPI is top shelf.
Here are some links to help get you started. Hope this helps, good luck!
SHANY Nail Art Set (24 Famouse Colors Nail Art Polish, Nail Art Decoration) https://www.amazon.com/dp/B005X2F7KI/ref=cm_sw_r_awd_8gaEub1TK3HVR
DragonPad 5pcs 2-ways Acrylic Uv Gel Nail Art Design Tips Dotting Painting Brush Pen Set https://www.amazon.com/dp/B005Y6F4WO/ref=cm_sw_r_awd_AtaEub111WR7A
Nail Art Brushes- Professional Nail Art Brushes- Sable Nail Art Brush Pen, Detailer, Liner **Set of 3 https://www.amazon.com/dp/B007BLN17K/ref=cm_sw_r_awd_IyaEub19FMKQ2
1200pcs New Nail Art Rhinestones Glitters Acrylic Tips Decoration Manicure Wheel https://www.amazon.com/dp/B008RS4LO8/ref=cm_sw_r_awd_1AaEub1NFX4D9
OPI Natural Nail Base Coat & Top Coat COMBO FULL SIZE .5 https://www.amazon.com/dp/B004B3YC9M/ref=cm_sw_r_awd_PBaEub19KD7J8
I can't win both?! LAME ;)
El cheapo BRUSHES. I've decided that you can't have too many of the skinny ones :)
I just realized you specifically said POLISH. Lol. Here's the cheapest polish...though I feel like the prices change every time I click on my WL
Llama face. Llamas are pretty, right?
Heard these were great! I also LOVE these for getting super slim, clean lines around the cuticles!