Sorry for your loss.
You might be able to do a factory reset but you'll need the Gmail account credentials

 

sorry but unfortunately without knowing the password, pin, or pattern, the only option to get into the phone is by factory reset. and a reset will delete your data on the phone.......there is no way around it.

 

Just to emphasize what's already been stated, a Factory Reset will delete her data. That's what a Factory Reset is designed to do, wipe user data off the internal storage of a device. So if there's any chance any family member or friend who was close to your mother might know what password she used, DO NOT do a Factory Reset if you want to get access to that Redmi phone. If a phone's lock screen was to be easy to bypass, it wouldn't have much of a purpose.

Do you have access to her online Google account? Keep in mind that the lock screen on her phone is independent from her Google account but if you can at least access her Gmail, calendar, and contacts (presuming she had her phone set up so those items automatically synced with her Google account) that will be something. Also do you know if she had the Google Photos app on her phone, and if it was set up to sync with her Google account?
Getting her text messages could be much more involved and difficult, and dependent on which text messaging service she used along with which app.

You can use Google's Takeout service to do a full backup of her Google services data. Select the items you want to have backed up, and there will be a resulting zip file that may be several GBs in size depending on how much stuff she had stored:
https://takeout.google.com/settings/takeout?pli=1
If you do not have access to her Google account, there is a lengthy process for loved ones to get access. You need to authenticate yourself and provide proof your mother passed on. It's a cumbersome process, but accessing someone else's account is a major deal.
https://support.google.com/accounts/troubleshooter/6357590?hl=en#ts=6357650

My condolences and very sorry for your loss.