Congratulations on becoming a grandma/granny/nana.
I'm so sorry to hear what an awful experience your daughter had giving birth. This sadly seems to be a lot more normal now.
I too had the most horrendous first birth with my daughter. In labour for days, couldn't sleep and couldn't keep anything down, so was completed exhausted. Junior doctor on shift, on his own, when I was 10cm, he knew I was struggling to get my 'back to back' baby out, didn't ask for any help or back up, decided to send me down to theatre for forceps delivery, at the same time he sent someone else down for the same. I was left shivering in a freezing cold theatre, and he was nowhere to be seen. My baby's heart rate started dropping. The alarm was going off, everyone panicking. Baby heart rate was played out on loud speaker, for all to hear. It was terrifying. Eventually he came in, was busy fussing over paperwork, before he finally delivered her. In the process he sliced open my bladder, but wasn't sure, so just stitched me back up, then it became apparent he had sliced it open. I was then left with no food or drink, for another 12 hours, having CT scans and generally just waiting around, until they finally operated on me again to repair the damage. I had a catheter for 6 weeks. Was kept in hospital for nearly a week, and loads more awful things happened to me there.
Anyway, I remember how low I was after the first few days. I had a mega dip in my mood and was really upset and emotional. I was frightened etc, but after about 2 weeks and when I was at home, I started to feel better. Now, exactly 5 years later, I don't even think about it. I didn't need counselling, talking to other people helped. I did complain to the hospital, which helped too, as they wrote back to me with a response to all of my complaints, and apologised. I didn't want a birth debrief, as didn't want to see the people that had ruined my birth experience. I didn't feel it would help. I did also get legal advice, and it was confirmed that my baby would've been born by forceps delivery, had the doctor not been so cocky and asked for help and not left me until it was almost too late.
I hope your daughter is ok. It's so normal for low mood after the first few days. Hopefully after a couple of weeks she'll be feeling much more positive, once things settle down.
Just be there to help if she wants. I didn't want anyone to take my baby and give me a break. I just wanted her with me all the time. Maybe because of what had happened. Maybe because I don't have my mum anymore - maybe I would've let her take her. Just see how your daughter is. Offer but don't force.
Good luck to you all and enjoy the precious new bundle.