Someone said :
There's no law, but every reputable college either forbids it or strongly discourages it as a conflict of interest and having the potential to be an abuse of power. If the lecturer is responsible for supervising the student in any way, it's always forbidden.
So it's best to stay well away at least until you're not her student any more to avoid making things difficult for her. She is unlikely to be receptive, if only for the sake of her career.
Yes, as a lecturer I can confirm this. It is considered unethical for a lecturer to have an intimate relationship with their student on the grounds that such a relationship can lead to a conflict of interest and almost all third level institutions forbid student-teacher relationships for this reason.