Sorry to hear of your loss. Unfortunately, if you have entered too many passcodes, the phone may be in a state where it is impossible to get back in without erasing and resetting the phone, wiping any data that is only on it.
Hopefully your mother was synchronizing data to iCloud and/or backing up data to iCloud. With the right legal documentation, Apple may be able to help you gain access to her Apple Account. If she, say, was using iCloud Photos, once you had access to her account you could log into https://www.icloud.com/ to see, and get, them. (With backups, the way you see what is in one is by restoring it to a device, wiping that device in the process.)
The following may be helpful:
How to request access to a deceased family member’s Apple Account - Apple Support