Lost password

Hello. Before text, sorry for my english.

The situation: I had iPhone 5 many years ago. After me, my niece used it, she was about 9-10 years. She (maybe with her mother’s help) made her own apple account, and now, when I get the phone back, she forgot the password because she didnt use it too much to remember important information, and now I cant exit iCloud and other services.

Can u help me with it? I have only her email on screen, and the box from device to show u I didnt steal it :D