"DH doesn't mind whether she comes or not but he's not the one entertaining her and he wouldn't dream of saying no."
Here's the thing. You need to talk to your DH about this and make him see it can't all fall to you. Be specific. Set the dates of her visit and talk to him about blocks of time where he HAS to be looking after her. Don't just say "don't be wandering off all the time". Say "I need you to be taking care of your Mum on Easter Monday morning till at least after lunch." (or whatever)
I actually think you should let her come but I think you need to find ways to limit the resentment. Bereavement is brutal and big holidays are the worst time. Let her have Easter weekend with you but plan it like a military operation so you can stand it (or even enjoy it!) and cancel your days off for another time.
Talk really clearly to DH about him stepping up socially.
Arrange get-outs as if prior engagements where you can go off alone (or with a child or two? Sorry not sure how many you have and how old they are.) Be really breezy about your "pre-planned trip to visit friend" / "do some house admin thing" / "trip to the gym" (either real or just sitting in the park with a coffee and a book, up to you).
When you are with her, don't allow her to dominate you. Plan the meals (get DH to do as much cooking / going out to eat as you can) and if she says "I like x with that" just say gaily "oh really? We've got peas today!" and get on with your life (easier said than done, but grit your teeth and PRACTISE)
Get her talking. Ask her to bring some old photo albums or dig out whatever old photos DH has and make her sit with them and talk about everyone. I find this more interesting and less annoying than having people clinging onto my life and what I am trying to do which they don't really "get": instead, go to her areas of interest and sit there for a bit, and you can "be" with her more rewardingly. Also, this gets the awful soaps off the TV. (It is easier to do this if you have had a break - which is why you need to build in your time away from her so that you can do this)
Don't let her dominate the TV. She is a guest of your family. This is rude. Talk to DH about this in advance and come up with strategies to stop this.
"I feel mean for thinking and saying all this but I just feel backed into a corner"
by everyone. Find ways of doing things on your terms to feel better about it. Make DH understand how this takes its toll.
"but don't see why it should fall to us either when her other DC's both have 5 bedroom houses but I see this happening every bank holiday. Whilst they are away every bank holiday weekend. She is retired so could visit anytime."
Ok you need to talk to the others. Don't let it happen every bank holiday. Phone them, or get DH to phone them now and say "we're very happy to host mum this Easter. Obviously this is a tough time for now that Dad's gone. Can we look ahead over the next year and think about who's going to be with her at certain times?"
Does your DH have any idea how hard this is for you? You might be making it look too easy. You might need to cry