Hi again Eddie,
If you are adding tripe to Pedigee Chum you should be adding some biscuit meal to bring it back into balance.
Bear in mind that more dogs are overweight than underweight.
If you do want to put more weight on her, give her as much as she will clear up twice/three tiimes a day. You will probably find that her appetite will shortly reduce - a growing dog need less food than a full-grown one.
If she has not been in season yet at 9 months, you will probably not have to wait much longer!
Walter