Welcome to Android Central! "The latest version of Lollipop" is an oxymoron.

Lollipop is extremely out of date (a full 7 versions behind the current Android 12), and has been losing compatibility with a lot of apps lately. Apart from everything else, it would be very much advisable for your mother-in-law to upgrade her phone, both for security's sake and to make sure she can still use the apps she wants to use.
Regarding her photos, does she use Google Photos to backup all of her photos? Tell her to go to photos.google.com on her computer browser and see if the photos are there. If not, then does she save the photos to Internal Storage or the SD card? If the SD card, then it's possible the card might have become corrupt, in which case the data is probably lost (SD cards are inherently much less reliable than Internal Storage). This is why it's always important to backup or sync important data on a regular basis.
Regarding the date & time, is she still using this phone as a phone (i.e., is a SIM card inserted)? Or is she just using it as a wi-fi only device?