My sister used to have an iPhone 4 that I used before (she replaced the battery); she's used it until 2013 or 2014 when the battery was not usable anymore. She's then used an Android phone for a few years and has just bought an iPhone SE. She wanted to restore it from iCloud but the phone shows "no backups available" once she logs in to her Apple ID account during the initial phone setup.
The iPhone 4 had newest iOS 7 installed, I'm not sure what version the SE has but it may even be 12. Does Apple delete old backups if no one logged into the account for a few years? Or maybe restoring from a backup to iOS 5 versions newer is not possible? Are there any other reasons it may not work?
I'd normally try backing up the iPhone 4 again but I think it doesn't survive long enough to back up right now, even when connected to external power.
I'd appreciate any help.