I'm a bit worried about some of the advice here.
Anyone involved in mental health will be trained in safeguarding, if there are concerns over your granddaughter, they will have been raised already.
Many families are spending a great deal of time at home right now, as long as your granddaughter is loved she will be resilient enough to cope with that. She has socialisation at school.
If you call social services, you run the risk of your daughter guessing it was you. You will lose her and your granddaughter if social services become involved and find no issues.
As for her husband, he is not enabling her, he is supporting her, she is doing the right thing and getting help. If he were to push her, she may very well go backwards.
I think you need to take a step back and just offer positive support. You may destroy your relationship for good on this path, when your daughter is already pulling away from you.
I'm sorry but the way she will probably look at it is you being controlling or seeking revenge. Two years and you didn't report her, she pulls away and suddenly she is investigated, that's very easy math.