My advice is any Amazon seller, unframed, $12-15.

A lot of PBN online ships from China, so watch the shipping dates closely unless you have a couple of months.

AliExpress has a huge range of fun, modern patterns (like star wars posters and stuff like that, because they don't care about copyright at allllll) but they do take 6-12 weeks to arrive. Fun for yourself but probably not great for a gift.

Either way, all the brandless online ones you get are 99% the same thing in the box. They're fun.

Make sure you are buying acrylic PBN and not diamond pbn. That's a different craft but search results mix them up.

Converting art to a pbn pattern causes it to lose a lot of detail. Sometimes people advertise with the original but the final pbn is kind of blobby. You can look at finished ones in the reviews sometimes. A portrait with fine stray hairs will not look that detailed in pbn, but something cartoony usually translates very nicely. I did a super fun boho cow that came out awesome because it was meant to be chunky. I'll see if I can find a link when I'm done to explain it better.

I try to avoid anything with a majority of white in it because painting multiple coats of white on white for hours is a drag.

It's all fun otherwise. Hard to know if she has a preference for landscapes or portraits or whatever. And even if she's done a bunch of landscapes she might appreciate a change of pace.

Other things you could consider gifting a pbn person are a nice set of detail paint brushes from any art store, a bottle of acrylic retarder (not expensive; it keeps the paints from drying too quickly), a white gel pen (for coloring out the numbers before painting so you don't need to second coat as often), a giant clip board or easel, and a good audio book.

Edit: the cow YEESAM ART DIY Paint by Numbers for Adults Beginner Kids, Colourful Cow with Flowers 16x20 inch Linen Canvas Acrylic Stress Less Number Painting Gifts https://www.amazon.com/dp/B07HFSNHV6/ref=cm_sw_r_cp_api_i_RlraDb53QB3CZ

One I'm doing now that's coming out pretty well YEESAM ART DIY Paint by Numbers for Adults Beginner Kids, Roses in Glass Dome, Enchanted Rose Flowers, Beauty and The Beast 16x20 inch Linen Canvas Acrylic https://www.amazon.com/dp/B07HFT21CJ/ref=cm_sw_r_cp_api_i_nmraDbMCWT90F

One I did last year that's lovely Colour Talk Diy oil painting, paint by number kit- Peking opera 16x20 inch https://www.amazon.com/dp/B00KQFMMYG/ref=cm_sw_r_cp_api_i_0mraDb0178SN5

In contrast, here's one I started that lost so much detail I ended up not finishing it: CaptainCrafts New Paint by... https://www.amazon.com/dp/B073WXBTGK?ref=ppx_pop_mob_ap_share

Hope that helps!