How can I link 2 iphones to 1 Apple ID?

2 weeks ago, I changed the password to my AppleID, not thinking about the fact that my mother's phone was linked to mine. For context, she has an Iphone 5 and I have an Iphone 7.

Since I have changed the password, she can no longer access her phone, and her device no longer appears on mine.

Is there any way I can relink her device to mine? She lives 7 hours from me, so I can't physically see what's up with her phone.

If anyone has had this issue in the past, and could help me out with some advice, I'd be so grateful.

Thank you