How do you respectfully remove someone from your research group?
How do you respectfully remove someone from your research group?


To answer the question literally, although there is no nice way to do this, you can be respectful by sending a brief, straightforward email (and do it ASAP): "I am sorry but due to changing circumstances I don't think we can collaborate more on project X. I wish you the best in your future endeavors and I'm very sorry for the unexpected change."

However, your real problem is (as others pointed out) that you seem to be an awful mentor: although you have given no indication that there is actually any barrier to the student helping on the project, you (1) told them they could help, and then (2) mentally retracted that offer, apparently without them doing anything to make a bad impression. So retracting the offer here is highly unprofessional and unkind.


  Now, I've realized that there really isn't much that she can contribute to the project besides stick around and do manual data entry


Can you really not think of anything she can contribute? You offered originally, so you should see this through and help her get up to speed. It will be a learning experience for her and an opportunity for you to become a better mentor.


  I feel like it'd be unfair because I would be doing everything


You seem to just assume that you will do all the work; you do not seem to treat the student like a collaborator, i.e. with respect and thoughtfulness.


  but she would also receive the credit for it (and my "contribution" would therefore be viewed as less).


Your focus on only your reputation here is telling. If she really doesn't help with the work, she should not be on any papers you submit at all, but instead you are worried about saving face and you would consider putting her name on a paper without her helping at all?


  I'm not sure how to tell her that I don't want to work with her anymore in a way that she wouldn't be offended, but also in a way that doesn't make me look too bad for "going against my word". Any suggestions?


There is no way. She may be offended and you are going against your word. However, that doesn't mean there isn't a respectful way to do it, which I have suggested at the top of my answer.