Should my husband be the one to tell his mom she is moving from rehab to long term care, or let the social worker do it?

Let the Social Worker do it and say it is based on medical decisions, not your wish but medical necessity. That way you are not the bad guy. Good luck.

(((((hugs)))))))

I vote for the SW, with your husband in attendance. They seem to take it better from a non family member,

I think I would arrange for the SW to discuss this with MIL while DH is there. The social worker can talk about staying in LTC to get stronger, so see how she progresses.

It can be "this is what the professionals think is best, mom. We can't give you the kind of care you need in a private home."