you want us to believe that she regained her ability to menstruate from kissing her student? really now? even if that were the case, i am pretty sure menstruation doesn't works like that, and it takes way longer than that for the egg to travel down.
If anything like that is what happened here (and I think it'd be a more general "her ovaries have stopped malfunctioning" rather than "she's immediately ovulating because of this one event", I think it's only meant to be a dramatic significant. Myself, I wouldn't care to analyze the literal mechanics too much when the condition itself is plausible.
That said, I can't say that I'd appreciate it too much-- it'd be an element that's both introduced and capitalized upon in the same chapter. And for a character that intensely focuses on her sexuality (albeit in a dire way, given the circumstances), you'd think her amenorrhea would be something she was aware of well before she saw her friend pregnant. But even that can be justified-- after all, the only sexual contact she's experienced until now has been forced on her.
