I agree with JCJ. Use this as a time to do some DBing. She may even be expecting a reaction from you(if she knows she has done wrong), don't give it to her.
When I find myself assuming things and my thoughts start getting out of control I use the STOP sign tenchique that SM mentioned and then ask myself What evidence do I have to support this? If it is none then I try and let it go.
Me-27 H-28 M-2.5 yrs T-8.5 yrs No kids B 1/09 S 2/09