OP - I really feel for you. You are a good person, because you are well aware of how your m-in-law must be feeling after her bereavement and you are prepared to host her visit even though you are feeling exhausted and she is a difficult person. You have done a great deal to keep the family together despite her problematic attitude and behaviour.
I agree with the comment that you do reap what you sow and if she has been unpleasant to you in the past, it is hardly surprising that you are finding it hard. I think you need to ask yourself:
If you were going through a really tough time or a bereavement, would she put herself out for you if the positions were reversed?
Has she shown consideration for you and your feelings in the past, or is it all about herself and your dh?
If the answer to either is no, you are giving a great deal to let her stay for the shorter time over Easter.
IME you also need to ask yourself, if you are feeling at the end of your tether during a visit that is too long, is there a danger that you will say or do something in the heat of moment when angry or stressed that will cause much greater upset in the long run? I have found that if I am pushed too far, it is a good idea to withdraw because I need to cool off and have some me time. From what you have said I think your family are desperate for a break and that should be put first.
Finally, I totally agree with all the other posters, your dh has to step up and take responsibility. It is outrageously unfair otherwise and he should not be allowed to get away with it, because, as others have said, this could be the thin end of the wedge and you could end up hosting her every holiday. Stand up to him and her and make some demands of your own, please.
All the best..