Responses
For what I remember in the novel, she does not 100% regain the memories of her past life, she has some feelings for Katarina, but she is selfless, and would rather support her brother with Katarina to play it safe and become Katarina's sister-in-law.
Bear in mind, I have read the novel until what was the "ending" at the time, it does seem the novel is still on going, it was after the party where Maria was supposed to confirm her feelings for the target.

I thought she was shipping her brother with Katarina(⌒▽⌒)