Q: if i change my password on itunes on one devise will i be required to change password on other device

Well, she will not be able to do anything if you have changed the password and she doesn't know what it is. Why not set her up with her own Apple ID and use Family Sharing? If you are running iOS 8 on the devices, and you set up Family Sharing, you can set it up so that you have to approve any purchases she is going to make:

Overview:   https://www.apple.com/ios/whats-new/family-sharing/

Set up Guide:   https://www.apple.com/icloud/family-sharing/

Best of luck,

GB