First, I'm pretty sure Tifa knew from the start that her mother had died. In despair over the loss, she just decided to do something rash while painting a picture in her mind that she'd be able to meet her mother again. (I don't think it was in an intentionally suicidal way--but intense sadness can make you do some very illogical or dangerous things.)

Anyway, with a fall like that and such an injury that caused a coma, it's likely Tifa doesn't remember the moments leading up to her fall. In fact, the entire ordeal ends up being kind of a blur to her - "So that was it...... Sorry, Cloud. If I had only remembered more clearly
what happened, I could have done something sooner......" With so many traumatizing things going on for her at once, it's a definite possibility to forget to ever mention something like that.

Also, Tifa may have not even known about Cloud's lecture from her father anyway. She was unconscious at the time, and Cloud probably would have been too shy/embarrassed to bring it up to her or anyone in the future.