[dudul]

If you have a few witnesses of your interactions who can confirm that she tried to play the sexism card while you were behaving perfectly appropriately then yes you should mention it to HR to be proactive.

HR doesn't care about you or Sarah, they care about helping the company. If you already have a "case" (ie witnesses) and approach them first, then they will see you as the "safer" party to side with.

If you don't have anything solid to back your story, then it's a bit more risky and it may be a better move to not do anything and hope that she won't take any action.

In the future, you should definitely be very careful to properly document your interactions with her though.