Background: parents divorced when I was a kid. Lived full time with mum. Thought she was great but in hindsight she was anything but.
In recent years we haven't had a whole lot of contact. It dropped off and I stopped bothering because my calls and emails went ignored (I live in a different country now).
I had a baby a little over a year ago and although she seemed genuinely thrilled she seemed to be all talk. We were going to Skype all the time, she was going to do this or that but in reality she hasn't bothered with my DS. She didn't send him a present or card for his first birthday (just a Facebook post saying happy birthday!!) and nothing for Christmas. She did come to stay with me after the birth to help but she literally did nothing. I ended up waiting on her and she was a huge hindrance.
Again, I stopped bothering because I'd send her little updates and pics and I'd never get a reply. But when I put anything publicly on Facebook the amount she gushes is actually weird. 'This is the best. Nanny loves you. I love you all. I miss him SO much' sort of thing.
Out of the blue shell make contact. It'm usually left feeling guilty. She phoned me the other day when she'd know I'd be at work to tell me she was in the hospital (nothing serious). Because I was at work she said she'd call back later. She called later that evening and told me that she was pretty sure she was dying the day before. Wanted to talk to DS (17 months old with no idea who she is. He wasn't interested). She asked for a video so I sent her one. Then she says she was watching it all through the night and it really made her happy.
We went home last year to see family and we made plans to see her before we left which she just didn't turn up to. I then got a message saying she forgot she had to do something else.
She treats my db in a similar way. Rarely speaks to him. Plans to meet him and then just doesn't turn up with no real excuse.
She relies on everyone thinking she's a bit flaky but I think she's extremely selfish. I have other examples but don't want to write an essay lol.
I just don't know what to do. Voicing an opinion hasn't gone well in the past but it's actually really upsetting me. My DS is such a lovely little boy (totally biased obvs lol) that it really hurts that my own mother seems to just want to appear to be the perfect Facebook granny. Then obviously there's the sympathy she gets because she can't see him all the time and what not. And I feel like the worlds worst daughter. Eventually DS is going to realise he has a nanny who sometimes thinks he's wonderful and sometimes ignores him. 
Sometimes I feel justified in my anger and then others I feel incredibly unreasonable.
I appreciate it if you got this far!