This fills in quite a few things. D was the one I was waiting for the whole puzzle - 35 of those, plus six F's and five K's.

“I kne- Old Shep -as going to die before I started page one.”
“Don’t be ridi--lo-s,” the tea-her snapped. “Ho-?”
I shr-gged. “Be-a-se the dog al-a-s dies. Go to the librar- and pi-k o-t a book -ith an a-ard sti-ker and a dog on the -o-er. Tr-st -e, that dog is going do-n. -hat happened to Old -eller?”
“Oh, all right,” the tea-her ad-itted. “So Old -eller died.”
“-hat abo-t So-nder? And Bristle Fa-e? Don’t forget -here the Red Fern Gro-s. The do-ble -ha--- – t-o dogs die in that one.”
“-o-’-e -ade -o-r point,” gro-led -r. Fogel-an.

Fro- No -ore Dead Dogs
B- Gordon Kor-an

Moesha: R (29); L (16); G (19); D (35) = 99
Catty1: E (53); I (21); O (46); A (32); S (19); P (8); K (5) = 336
Karen: T (35) = 35
Felicia's Mom: N (23) = 23
Asiel: H (22); F (6) = 28
cassiesmom: B (9) = 9

Letters left to guess:
CDJMQUVWXYZ