Yes I see what you mean and why you are asking. I know I posted something about yr MIL being manipulative. I don't know a great deal about bi-polar. I suffer from intermittent depression and anxiety, and for me I canot help feeling flat and empty and miserable when it strikes, and attempts by anyone to "cheerup" just make me worse, as I know how much I want to be "me" but am not able to be.
On balance I would say that no one can "help" having any mental illness, be it bi-polar or anything else, and in its acute phase then NO I don't think anyone can help feeling as they do (but i can only speak from my own experience)
The thing about your MIL is that she seems to have decided that it isonly her son who can help her - thus she is wanting her son to parent her and that's the difficulty because he cannot fulfil this role. Also the thing about trying to attempt suicide in front of him could be seen as manipulative, but it can also be seen as a "cry for help" or to demonstrate how bad she feels, or just to keep him with her (which is manipulative really) Two big changes in her life have occurred - retirement of the old GP who understood her and the new one who will have a different view, but might be more up to date in drugs for bi-polar. Also your move to the Midlands from S. Yorkshire, which must make her feel abandoned to some extent, hence the 20 phone calls. I wonder if there is a deterioration in her illness because of the move away, but there again this could be because she feels bereft and that has caused her deterioration. I do however think that she is to a large extent trying to make you dh feel guilty, and of course she is succeeding.
I honestly don't know - mental illness is such a strange illness and I think it's probably true that some mentally ill people have some emotions in common, it is also very individual.
Sorry I can't be more helpful......I'm going round in circles. Incidentally I live in the Midlands - do you want to PM me to let me know where you are, though of course it's a big county. NN x