Rfs
Im not sure what you mean by “things” but if you know for a fact that the guy either still has connections to other girls or the guy has other problems that can impact a marriage (like a gambling addiction or other addictions) you have an obligation to tell her. Don’t be afraid of the consequences (the Shidduch may be broken) because a Shidduch under false pretense is a sham. The marriage will end in divorce as many others have where one side was still busy with their twisted past and wasn’t mature enough to move on and be a responsible spouse. I would consult a Rav first. No not his Rav but one who isn’t connected to either party so that he can give you a totally unbiased opinion.
Maybe speak to Rabbi Wallerstein. He has a lot of experience with these things.