Replace the entire computer if you can... Anything they talked with or shared...

Did she change her email address? Cell phone number?

Change it... Change is how she makes progress here.. if she hasn't changed anything she isn't going to get past this...

This is still high risk... People who end affairs but struggle with the withdrawal have this pesky habit of getting the idea that because they can't easily forget about their OP that they are "meant to be" and they run off togehter ...

She has to put up LOTS of WALLS to shut this guy OUT

If she hasn't done that then she's got a much stronger chance of relapse