Undermining an Arguement

Thomson uses the example of the violinist to argue that abortions are sometimes morally permissible, specifically in cases of pregnancies due to rape. One major premise of her argument is the assumption that the violinist is analogous in all morally relevant ways to pregnancies due to rape. This is perhaps the most controversial premise in her argument, as there are several differences between the violinist case and pregnancies due to rape, differences that some have thought are also morally relevant.
If you choose to write on this prompt, complete the Expository Task for it, or specifically:
First: Explain Thomsons argument, based on the example of the violinist, for the conclusion that abortion is morally permissible in pregnancies due to rape.
Second, brainstorm one (or two maximum!) difference between the violinist case and pregnancies due to rape that you think could potentially be a morally relevant difference. Describe the difference you have in mind and explain the reasoning behind thinking that this difference could be morally relevant and thus undermine Thomsons argument.