I have 3 ipads and want to change the apple id on one.

Is she using your Apple ID for Facetime and messages? That would be confusing, as that would be your email account. and name being used for her messages.

She should in all honestly have her own Apple ID. Apple IDs should not be shared.

You can set up Family Sharing to continue to give her access to Apple Music and your purchases.

click here ➜ Make sure that each family member has a unique Apple ID - Apple Support

Depends on what you want to change the Apple ID for specifically.

The iPad is logged in to an Apple ID in 4 different places.

Settings ➜ Apple ID

Settings ➜ Apple ID ➜ Media & Purchases

Settings ➜ Messages

Settings ➜ Facetime

The one in Media & Purchases is what controls access to the subscriptions like Apple Music.

If you change that, you will lose access to whatever the original Apple ID had, and gain access to whatever the new Apple ID has.

Messages and Facetime will work on the new Apple ID you use with them, but you would stop getting messages and calls made to the other Apple ID.

What exactly are you trying to accomplish by changing Apple IDs?