I had the same problem with Kat on that level. Odd.
And legendary isn't too bad on a whole. Only two parts I got stuck on are the "last level" already discussed and the part instantly after the space combat with entering the Covenant ship in zero G. I beat it legendary on my first play through in two 5-6 hour sittings and I'm by no means a Halo expert.
I will admit though that the part just before the credits was irritating!







