apple id issue with line

This is a bit complicated but i do need some advise.

current situation: an line app was installed on my mom's iphone a while back and she has been using it for a while. At that time she was using "my" apple id when downloading the line app on her iphone. Now i created her own apple id and she has an ipad so i install line on her ipad using her apple id.

question: first, is it possible to change the line on her iphone using her own apple id so she doesn't need my apple id whenever downing new updates. second, in her ipad how to login to her account and have all the chat history like her iphone has.

thanks!