Of course, unlike Alice, Desiree knows better than to come out and tell an assassin that she knows he's an assassin. This way, if said assassin is there for her *I imagine she's made a lot of enemies, which is why she's changed her name multiple times, her appearance cosmetic-wise... (I imagine a spell or potion to change your hair color and such isn't hard to come up with) multiple times, and faked her death no less than three times*, the assassin will be operating on the false assumption that she doesn't know who he/she is... and that means that Desiree would be able to catch that assassin off-guard.
Naturally, she also keeps extra-vigilant to make sure the assassin doesn't know that she knows... because if he/she does know, then she has to pretend she doesn't know that he/she knows that she knows he/she is an assassin... and so on and so forth and on and on.