Can you ask her for help, such as, I'm kinda struggling for ideas and I'd like to get you a couple of bits to open too, would you like a wreck it journal? and then if she says yes you can choose one so it's still a surprise. She might say no, or say actually I really wanted this.. idk but I definitely had strong ideas at 12 what I wanted lel but everyone is different!
My mother is going thru this at the moment, I get them to write lists for me and then I pick the items off it to fit my budget. For me, I have to literally link them to ebay items or websites, and they get me the exact items, because the struggle is real and left to our own devices we just don't get it right lol
Maybe she wants vouchers as she has her eye on some things, but doesn't like to say.
She is probably super interested in various things, and if you listen she will mention them? Putty or slime kits, Idk I'm horribly out of touch, but maybe there's some things she's really into that you could get her stationary or stickers or something that matches? Like you can get Harry Potter merch so cheap on ebay as it's not the exact brand. Or Primark sell smaller items cheaply too like socks. I don't know your budget, but u can make any budget stretch really far with online stores. Depends what she is into
Btw, when I was a 12 year old all I wanted was Sea Monkeys, and I never got them lol