You are not being unreasonable.
Your DH is really, REALLY not helping her.
Maybe get him to read this thread?
This could be her life situation for 20, 25 years. She HAS to forge a new workable life. It's been nearly a year, that's a good time to start - and if the only way that will happen is if your DH 'forces' her to, by starting to pull back - then he must. If he really, genuinely wants her to be as happy as she can then he must, even if it's hard. Another few years of this and she will be a shell - she will retreat, permanently into herself and not only will it possibly destroy your relationship and have a terrible effect on your children long-term... it will also render your MIL helpless, friendless, and unhappy.
And then there's you. This simply isn't right - there is a difference between supporting his parent and totally abandoning his other, more important commitments. They ARE more important, too - his marriage, but most of all his childrens' wellbeing. What is the use of supporting one family member so much that others who genuinely depend on you are damaged?
It is a really silly situation. Not only is he actually hindering your MIL's grieving process, he's destroying his own family. Show him this thread.