Thank you for responses.
I didn't really want to go into depth details about our personal situation / DMs but possibly without the background, the post would come across in a different light. Let's just say i'm 90% certain my DM does not have many of the issues she is claiming for - certainly not issues with being around people in public. She is very good at putting certain things on in certain situations & various health professionals have agreed. However - I appreciate that without giving any further detail on this (which I'm not) people can see it as just an attack on a poor person with MH issues.
I would like to say a massive well done to Poodle and others similar - I did try to say at the start, this is certainly NOT an attack on those who want to work, are trying to get back into work or would love to but really can't because their issues are too bad. My DM has barely worked a day in her life, through a mix of selective relationships with people who would fully support her & now the benefits. This in itself is also one thing, but she has no wish at all to do so, now or ever, and is actually scornful of people who do work so her volunteering is not a stepping stone or rehabilitation, though I accept it could be therapeutic.
Waffley - you made perhaps the most pertinent point, that just because you don't understand someone's condition doesn't mean it doesn't exist. Excellent point and one I constantly try to remind myself with her, and remind other people who get equally frustrated with her. I have always tried to justify things she does by her conditions but over the past few years have come to the same conclusion as my DH, grandparents & others that a lot of it is fabricated. Which, admittedly, is possibly a MH condition in itself.
Re: the childcare. When I repeatedly said we realise she had no obligation to do childcare for us & it's our problem, I actually wasn't just saying that for effect. We've always known it & at the point we decided to have Baby 2 - which is a complicated situation in itself - we did the maths, worked out childcare would take most of our salary & decided we were ok with that if needs must. We had started arranging childcare, then DM began asking if she could do it as she had nothing else to do. We had serious doubts - due to the MH issues history - but as we also have come to believe she's not as unstable as she claims, we considered it. Obviously the huge cost saving was very tempting too, I won't deny that. We said no to begin with as we didn't feel we could rely on her, but for about four months she continually asked and had tantrums if we said no. So we went through an odd cycle of looking for childcare, every time we found someone she begged us to let her do it instead (in varying combinations of amounts), so we'd cancel. She kept changing her mind on & off and using it to blackmail us, sometimes saying we were making her ill by saying no, sometimes we were making her ill by saying yes. About 6 months ago, I firmly made the decision not to use her to help, and as she lived so far away that was easy to explain. Then out of the blue, she sold her house to an agency, kicked out her partner of many years & bought a flat 5 mins away from us...it all happened incredibly quickly and with a lot of drama, because she insisted she wanted to look after DS. With her around the corner I felt it would be both unfair (on her) and stupid (for us financially) to not at least give it a try. So we turned down our childcare place. Cue lots of on-off mind changing, again not wanting us to find anybody until finally, with 2 months until my DS started school it came to w crunch as explained & we made the final decision, not her, that even if she changes her mind again she's not doing any.
So the bitterness is more to do with a long boiling sense of being messed about by a parental figure, rather than believing she has an obligation to do our childcare. Added to this the many many lies and dramas and it's exhausting. And yes, when she called me up to merrily tell me about her volunteering I did find the whole thing mind boggling.
But I accept - a) our kids have had a lucky escape and b) however much evidence there is to the contrary, on the 5% chance she could have severe MH issues, perhaps volunteering is all she can manage in life & it's better than her being in bed all day, definitely.
Not sure how people took it as me sneering at volunteers - they are an invaluable part of where I work, never mind other places. As I said - every situation is different.