Suicide is defined as the act of intentionally causing one's own death. There are many factors that play a role in influencing whether someone decides to commit suicide. Nearly everyone experiences suicidal thoughts at one point or another throughout their existence. 

Everyone deals with tough times, but some people have been dealt a tougher hand when it comes to life circumstances, past trauma, mental and/or physical illness, social standing, and ability to cope with depressive emotions.

People are most driven to commit suicide when they view their current situation as being completely hopeless and feel as if they have no way to change things for the better. Common causes for suicide include: depression, drug abuse, financial problems, as well as difficulties with relationships. 
Technically people who cannot face the challenges life has to offer will come to the conclusion the only way for peace to occur is death. Therefore not thinking rationally, they go with their gut feel. The mother you're refering may be deppressed, stress out and just tired of everything.