Will a relaxer damage my hair type?

I have very kinky (mostly nappy), curly hair and I am african american, so most of you know what I'm talking about. Will a relaxer ruin my hair? I have very nice natural hair and it looks really good when it's done professionally. My mom told me not to get one because of what happened with my sisters hair (it broke off and got very thin and short), but my older cousin has hair very much like mine and she has a perm which looks very nice (it's still thick and pretty). Everyone always tells me to not get a relaxer, but I'm very tempted to get one. Do you think that nappy kinky hair will turn out bad with a perm? And my mom would be applying it, not by a professional.