She thought that by killing him, she could stop him from killing anymore mutants and finishing his Sentinels. But there was some sort of message from the future that if she did that, the government would get their hands on her and use her DNA to finish the project anyway. So the intention was to stop that from happening.

[He may have been less than helpful in that regard, but it worked out in the end anyway. They already had Raven's DNA; what happened next didn't matter, or so he'd thought.]

Yes. We did.

[Those particular ones, anyway.]

The rest of them should never have had to go through that though.