I confess I don't remember hearing her at all. And I have good ears. 
The Jellyfish computer voice was definitely not Majel. As for the Enterprise computer voice, when did we ever hear IT speak?
Also, IMDB says that Majel provides the offscreen voice of Christine Chapel. I do know that Chapel is in the film - we hear McCoy ask her for something, and yes he does say "Nurse Chapel", and she replies (but is not seen onscreen) "Yes, sir." Was that Majel?

The Jellyfish computer voice was definitely not Majel. As for the Enterprise computer voice, when did we ever hear IT speak?

Also, IMDB says that Majel provides the offscreen voice of Christine Chapel. I do know that Chapel is in the film - we hear McCoy ask her for something, and yes he does say "Nurse Chapel", and she replies (but is not seen onscreen) "Yes, sir." Was that Majel?