I wonder if she assumed all along that she would assume, or if it came as a surprise?

All cheekiness aside, it is interesting all the different meanings that "assume" can, well, assume. [sorry, couldn't resist]. M-W lists the following

Etymology: Middle English, from Latin assumere, from ad- + sumere to take -- more at CONSUME
Date: 15th century
1a : to take up or in : RECEIVE b : to take into partnership, employment, or use
2 a : to take to or upon oneself : UNDERTAKE b : PUT ON, DON
3 : to take control of
4 : to pretend to have or be : FEIGN <assumed an air of confidence in spite of her dismay>
5 : to take as granted or true : SUPPOSE
6 : to take over (the debts of another) as one's own


Some of those are a bit redundant. e.g. Definition #4 seems like it is covered by "to put on" or "to don" in a figurative sense.