a rating drop is a pretty natural part or learning, in addition she can have a rating increase for a moment. I wouldn't be worried about that too much.
As for improving continuing to do tactics, and find some resources about middle game. I'm willing to look at some of her games and find a book about middle games if you want.
You may suggest her to look for games in opening of her favourite or say top player. This will open her mind to new ideas in midgame and better understanding of positional play. Hope she shines bright!! Happy to see you concern for your daughter's hobby, goodluck for your parenthood. You are doing awesome.
^^ Think about it. The kid is 8. She's not going to have a favourite player nor any concept of positional play.
1) play at least 15 puzzles
2) play 1 classical game.
Since I am not a chess player, how can I improve her game.
My analysis is she gets struck at mid games sometimes and gets frustrated.
Sorry for the long post