No matter what you decide, Star, I'm (we're) here for you, supporting you 150%. You're a mother first, I trust your feelings about this guy.
You're totally intittled to try to protect your daughter, also my opinion of her finding out the harsh reality by herself is obviously different.
Just... burn that letter and try to imagine it simply got lost. If indeed you decide to keep it from Krystall, make the "evidence" vanish
. It won't be to funny to have your daughter discover it by mistake.
Lots of luck, and do what Scarlett does when she feels guilty about something:"Think about it tomorrow!!!"
Love,
Twinkle