she bites the other cats too hard

My mom's cat meesha, whom they adopted in January and was 11 months old seems to not know how to bite gently. When she tries to play with my kitten, who is now 7 months old, Dynah screams which she doesn't do when she plays with chester (my 3 year old cat). Meesha also bites mom in bed when she tries to pet her. She seems to think it's playing or ok, but it's toooooo hard! She's even made mom cry.
How do we get her to bite less hard with the other cats, and not at all with us?
Thanks guys,
Jess