I had some trouble with this puzzle too. The last bit was a bit tricky.
I don't think the woman at the end is Carla. Carla was in EMI, and the voice is not a match at all. Sure they could have recast her, but I don't think they'd go with such a different voice for her. Kate Capsize seems more likely. The voice is a better fit. I don't think she carried a sword in MI2, but she was no push-over. It could be a new character, but what she says to Guybrush and the way they keep her identity a secret makes it more likely that she's a returning character. My money is on Kate.