I got a new i-pad for my wife and I want to transfer my data to the new one from my old one. However I also want to change my Apple id to hers. How can I do that?

Hello,

Apple does not allow two different Apple IDs to be merged into one and discourages the sharing of one Apple ID between multiple individuals.

https://appleid.apple.com/faq

Using Family Sharing can allow you to share subscriptions, content, and many more features without using the same Apple ID.

https://support.apple.com/en-us/HT201060

I hope this helps.

The data, purchases, photos, music, etc. is all tied to the Apple ID. If you are setting up the iPad using her Apple ID, it will contain her data only.