I’d recommend using a numworks. It’s a French scientific calculator that is “open source” and very high quality, all while being less expensive than a regular ti-84 which is the “standard”. It is very intuitive, so even if text books don’t show the instructions needed to operate it, she can probably figure it out on her own.
I’m in high school, and I’ve used this since 8th grade and it is honestly the best investment I’ve made for myself since it’ll probably me last for the rest of high school and maybe a bit of college.