My mum needs help? Is mental health issues hereditary?

I have known for the past few years my mum needs help. But how do I do anything about it when she thinks she is fine? She is a compulsive liar... serisouly, I'm not just over-exaggerating. ie; she is 51, hasn't had her period since she was 38 (common in our family) and now she is saying (to the what... 3rd or 4th b/f?) that she is pregnant. She can't get her stories straight telling me she has one baby and my cousin and SOME other family members she is pregnant with twins. Also, the most damaging of all lies.. she told her ex-b/f that my hubby and I used to bash our eldest daughter and she had taken custody of her from us and when I got her back she had to cook meals for her everyday 'cause I wasn't feeding her. Soooo NOT true! Not even the slightest amount of truth in it! I don't understand... And scarily, this sort of thing is frequent! I mean, on a daily basis. She can't even say she has gone to the shops and brought a loaf of bread without having been mugged or met a celebrity!