I think you should install the keylogger on the computer and TELL her you're doing it. Make it part of an overall transparency plan that you tell her you need in order for YOU to feel safe with her back in the relationship.
Ask her to do the other things, too -- change her cellphone #, send OM a no-contact letter, etc. -- and if she balks, you'll have your answer.
You hold all the cards here. Now's the time to play them.
