YouTuber RetroGamesCorp is pretty popular in the community and he's got a video with his favorite devices of 2023 that has a section for budget handhelds. He recommends the R36S. It will get you up to PSX smoothly.
In may of last year people were talking about a device called the DataFrog SF2000 which was incredibly cheap at $25. It has screen tearing and slow down for GBA games. I haven't heard anything about it in a while so I don't know if a custom firmware was ever released to fix some of these issues.
One other thing you might want to look into is picking up something like a DS Lite and flashcart because at that point you can play all NES, GBA, and DS games.
I would 100% steer clear of any of those 100 in 1 devices. Most of the time they are limited to NES games. Once you are tired of the few games they can play it's basically E-waste. At least with these other devices you can add games.
I think it depends on how long you think she'd actually use it. If it's for a couple months you could go for something like the Powkiddy V90 (the device people call a GBA SP clone) but if she's not shutting it off properly it can corrupt the SD card. You could still get the Datafrog and it might be good enough especially for Pokemon.