If she had been suicidal before, I would assume her parents would be well versed in the process of getting their daughter help... or maybe, like so many others... they simply didn't seek the help she needed at the time because of their own personal egos? So, they let her issues fester until she finally lashes out and hurts innocent people.
We could also ask whether or not these were actual suicide attempts or threatening suicide. One can argue that there are some people who like to manipulate others feelings by threatening suicide. For all we know, she could have been hell on wheels and herself and her family were just really good at covering for her.
Lastly, even if they were not Lyndon's clothes, it was something she consciously attempted to hide knowing it would be problematic for her. She knew exactly what she was doing and I agree with someone else who said that she's simply showing the signs of someone who not only got caught, but is in serious trouble. I am sure she is very distressed about THAT.