Why would my ex-girlfriend's mom friend me on Facebook?

My ex-girlfriend's mother, whose daughter is married, whose daughter's friends list I'm not in on Facebook, requested me as a friend on Facebook. While I'm trying not to read to much into it, it just strikes me as odd because I'm no longer conversing with her daughter, at any capacity, not to mention the fact that her daughter is married, when I asked her if her daughter put her up to that, she told me that she didn't, should I believe her? One more thing, I don't want to be rude and tend to friend most people that send me a requests because of familiarity but, the fact that there really is no connection between her and I other than her daughter, and I'm not even in her friends list, well, to me it just seems unusual.