Explanation of second line, which doesn't transition to English very well:

Maya nearly finishes her sentence informally, which would be unbecoming toward a superior officer. Thus, she quickly stops before the end and switches to the more formal "desu".

The "-tten" part was part of the informal finisher, which the admiral just tacks on to her name since he's presumably meeting her for the first time and doesn't know any better (or he's being a typical CO and just being a dick).

Just in case anyone doesn't know her original line, it's "Yo! Atashi, Maya-ttenda. Yoroshikuna!"