What Causes Severe Anxiety?

actually the problem is with one of my relative. she is 45 yrs old. she gets worried about very small things very easily and gets too hyper. if she is alone, she remains on thinking and goes in very deep about it. for even small problem the solution she thinks is to die.otherwise in normal time she is very polite and nice. actually she has suffered due to her in laws many yrs back and that incidence has made a place in her mind due to which she relates most of her problems with that incidence. according to me this might be her problem.and she is also very low confident