Once a Shared Apple ID, Lost Years of Photos After Making a New One, and Trapped in Family Sharing, Unable to Leave it

My mom and I used to share one Apple ID. I have since grown up and decided I should make a new one just for myself (for work, personal, etc). I backed up all my data from my phone when I was still sharing the ID with her (photos, messages, apps, etc.) before creating a new Apple ID, hoping to see something like "upload backed up data" or something similar. Except when I started my phone again (keep in mind this is all one phone, not a new phone, just my one phone), I chose to merge the data, thinking it'd bring everything over, but I lost years of photos instead.

I was determined to get them back, so I figured I'd try to join my mom's family sharing, hoping it would just load over. So I tried to create one from her phone, to which it says: "Family Sharing: Set Up." So I clicked it, and it says "[her Apple ID email] is already used for shared purchases in [my dad's] family. Ask [dad] to send you an invitation to join Family Sharing." So I tried from my dad's phone, but she is unable to accept that invitation because: "You're Already in another Family, you can be in only one family at a time. To join this family, you will need to leave your current family first." So I went into her settings to try to leave the original family (which might've been made from an older phone we used to have, but no longer have), but there is no button to leave. I followed the Apple instructions, forums, and everything I could find, but it is not there.

I don't know what to do if she is unable to send, accept, or leave the old family sharing (assuming maybe my parents made one in the past on an older phone, but never got rid of it) because the email that is tied to her Apple ID is also tied to another family's shared purchases, trapping her in that old family sharing without a way to leave it.

All I want is my photos and to family share with my mom's account in hopes of getting all of my backed-up data from the iCloud my mom and I shared.