Well the things she must know is the openings rules, the value of each piece and capturing, and she needs to play many games of chess, ofcoarse.
For her dropping pieces and not meeting opponents threats , it shows that she still needs a lot improvement in tactics. You should give her exercises of looking for hanging pieces, finding forks/skewers etc.
I think it's easy for a young 900 rated player to improve. And if you be patient and not expect drastic results she would quickly improve to about 1300 ratings in some months.
She's been playing chess for about a year and a half, in regular rated tournaments for almost a year. USCF Rating at just above 900. I'm the only coach she's had. Despite the mantras, she still has trouble hanging pieces on occasion and not paying enough attention to what her opponent is doing and threatening. She understanding the definition and half-pawn value of the Bishop pair, for example, but this type of knowledge is obviously not going to help her much if she's dropping pieces and Pawns. For her age, she's got a really good grasp of tactics and strategy, the tricky part seems to be in helping her recognize and meet threats.
Any chess exercise recommendations and other tips on how to help her get to that next level, where her game is relatively solid, would be much appreciated. Also, dos and don'ts for coaching a kid of this age and playing strength would be very helpful.
Thank you
-Tim