Sorry to hear about your niece. Unless you can use Android Device Manager, or whatever software your phone manufacture uses, to reset the password, there's no way to bypass the password without knowing it. The only other option to recover the phone to operational status is to do a "factory reset" in recovery. However, this will wipe all data from the phone... apps, vids, pics, docs, contacts, etc. Hopefully your niece has backed up her data to a PC or the cloud.
Watch this video (associated links are on the Youtube page). It has stipulations for the phone like having a Google account on the phone and being connected to the internet. While this video makes it seem easy enough, some people are not successful when attempting to reset their password. I wish you good luck.
https://www.youtube.com/watch?v=9yx_XGgrLVE#t=211