Co-author wants to remove herself in author list after revisions
It sounds like she withdrew from the paper, but not from the collaboration. In other words she's saying she doesn't trust the results of the paper enough to have her name attached to it, but not that she doesn't trust you. Therefore it doesn't mean the collaboration is over. Besides, if she contributed to your future work at the level of a co-author, she should at least be approached for co-authorship.

In response to her withdrawing from the paper, the best response is probably talking to the other co-authors, if there are any, about how to answer the reviewers' comments. If the consensus "best way" is unacceptable to her and she wants to withdraw anyway, then c'est la vie.