Masha was your boyfriend, Ilya's, sister. Well, adopted, as Ilya was only Natasha's adopted kid. The thing is she kinda had it out for him, due to their very different childhoods (and her extensive jealousy issues), and more or less wanted to kill him. She didn't seem to hate you though.

"Maybe try your hand with a different boy," Masha said, a little randomly, during a conversation with them one day. She was fidgeting with a pocket knife like you would a pencil. "One I don't want to kill?"