In Beka Lamb, why does Toycie become crazy?

In the book, Toycie's mental health is affected after falling pregnant and being spurned by her boyfriend, Emilio. To add to her grief, she is expelled from the convent school she attends.
Emilio's rejection devastates Toycie, because she always believed that he would marry her if she became pregnant. However, when she reveals the truth of her pregnancy, Emilio rejects her and callously tells her that he must finish his studies first.
Emilio also maintains that the baby can't be his because his "body didn't go into" her. Although the author doesn't confirm Emilio's words, we find his excuses suspect. Emilio also heartlessly proclaims that he won't consider marrying a girl who "played around" with him as Toycie did. So, after enjoying the delights of bedding Toycie, Emilio self-righteously proclaims that he can only marry a virgin.
Emilio's rejection and Toycie's subsequent dismissal from school is likely the catalyst for her depression and her deteriorating mental health.
Later, due to her depression, Toycie tries to commit suicide by jumping off a bridge. She is rescued by a soldier, however, and survives. Unfortunately, Toycie loses her mental faculties as a result of her suicide attempt, and she is committed to the Belize Mental Asylum. Much later in the novel, Toycie wanders off during a hurricane and dies after a mango tree falls on her and breaks her skull.