Preserving (Specifically) Procreate Files When Signing into a Different AppleID Account

So this is for my partner (M), she has an iPad that she creates art with on Procreate. M's iPad is signed in her mom's (C) AppleID account because when she got the iPad my partner did not have an AppleID account. M now has an iPhone and AppleID account and has run into the problem of never having enough room on her iPad (even though she has only Procreate and some social media apps on her iPad) and not being able to update her iPad or even her apps. This has made Procreate, the notes app, and even other apps start to crash or corrupt her Procreate files. This is because she is in C's account and it is linked, so her mom's storage is affecting her storage. Is there any way at all to transfer her procreate files to my partner's account?? That and her notes are the only things she needs transferred as all her photos are already on her phone. Her parents don't know how to do this either and neither do mine. My partner and I are adults so this is not something like her being on her mom's account as long as she is under 18. I've been trying to search up some solution for months but I cant find anything that would help. She has 3 to 4 years worth of procreate files on this thing and she doesnt want to lose these files. We both have the same Ipad so I listed it as my own ipad which is a 10 in. 8th gen.