Why don't you attempt communicating with her and try to settle things?
Seriously. Walking around with the mindset that you have does not defuse stalker situations. In the end, remember that you are dealing with a person who harbors intense feelings regarding you.
this person is mentally ill. no reasoning with insanity
How is she mentally ill?
shes obsessed, text me about going to see her shrink all the time. i dont know what shes ill with but glad i dont got it.
That's a weak answer. That doesn't sound like enough to consider someone mentally ill. So far, it sounds like she can't get over you and does not know how to deal with it. Unfortunately for her, you don't sound mature enough to address the issue effectively.