We need to break down the type of disorders, as causation is different in each one. Just for example, bipolar disorder, a genetically inherited mood disorder, cannot be “caused” by an abortion or by any traumatic experience. However, if one has bipolar disorder, certainly an abortion could trigger a depressive, manic, or even psychotic episode or series of episodes over the years, induce rapid-cycling, or any other number of problems that exacerbate the bipolar condition.
Contrast that with PTSD. You can easily imagine how a perfectly “normal” person with no predispositions to “mental” illness, no previous ailments, would suffer trauma (with effects of depression, anxiety, panic, insomnia, and even suicidality), due to the long-range guilt or shame or regret of destroying her child. This is also how agoraphobia can develop. Without treatment or some means of resolution (perhaps religion), these symptoms would likely intensify over time.