Bless your heart, mom. It must be hard. But the truth of it is that she needs to make a break now and make sure that he does too. The constant calling and texting isn't healthy for him. At some point it could morph into stalking her. If she allows this to string along, she could actually be enabling stalking behavior, and that's not good for either of them.
They both should date other people. Not serious dating, but getting to know other people type of dating.
Perhaps you could sit down and talk to him. Tell him that you care alot about him, and part of that caring is treating him like a "son". As your "son", your advice to him is to get out there and see what else is out there. NOT continuing to call and text her. Maybe he will respect what you're saying to him.
Don't allow him to pump you for info on her, though.
As far as your daughter is concerned, I think I'd tell her the same thing. You are supporting her if you are honest with her. She is doing the right thing by not responding to his calls and texts. It's kind of like the saying "It's cruel to be kind" if she lets him think that all this will make it so they get back together. She wants to make sure she doesn't string him along.
I think that's the best way to support her. At some point, she will start feeling some other feelings about the break up, but that's okay. Right now she just needs to separate from him and get out there and date around.
Sounds like peri-menopause - I wish you luck. Finally I crossed over into menopause-land with no periods LOL!! What is it they say, "When it rains it pours"? Smiles!