No, you are not being used . . . except as an admired role-model. Some people just never succeed at quitting pernanently. It's not a reason to "be done" with someone. Do you require that all your friends be non-smokers?

Now, if you are tired if being her quit-buddy, then just relinquish that role. But do it nicely. Tell her you hope she can eventually succeed, but that you being her quit-buddy is not really working and, so, she needs to use other techniques. What those should be is for her to figure out.

She is struggling and not just looking for attention. If you are tired of hearing about her struggle, then you can disengage from that.