So it sounds like you have a depressed DD. The correct response is not to moan about her grumpiness.
I'm assuming she's lost her school routine, lost her friends, had no time to herself, had no time without direct adult supervision, likely lost whatever it was that gave her self-esteem - even if she derives it from your praise, it's unlikely she's doing anything that enables you to provide, but by 8 a lot of kids are more external to the family 'cos they already know their parents will think everything their kid does is awesome.
As to what to do of course, that's much harder, we can hope, in fact I think we all hope that so much of the depression will start to go once schools return and the routines return, but even that is not for many months, but that hope also limits how interested schools and GP's are in child depression at the moment. I would still contact both though.
Otherwise, I'd see if you can find something that breaks the nothing-but-family routine you're likely in, find some activity that can be done with different people in a different group - is there anything she enjoys that is available, some club/activity something?