@Kightstark I guess when the first time they met, she thought that it's also part o a plot from the author where a 2nd female lead (rival) comes and pretending to be a boy. (I forgot is ruda is a transfer student)
For instance, other mangas have this plot about a female lead going to an all boys school and pretend to be a boy herself, in order to meet the male lead. So, I guess that's what she's thinking about.