Landlord took mail out of the mailbox!?

On April 3rd, on a Sunday evening as my wife and I were watching TV I saw a black SUV matching the landlord's pull up to our mailbox. By the time I went out they had left, and were at the top of the hill, but I was positive it was her truck, and our rent check that was in the mailbox was gone. A few days later she called my wife at her place of work and stated that she had not received the rent for the month of April, and swore she had not taken mail from the mailbox. The envelope contained a check for part of the rent, and a money order for the remainder. We called the bank and canceled the check, and I sent off for the money order to be traced and replaced if it was not cashed. I just received the trace results from Western Union, including a photocopy of the cashed money order, and the signature is clearly her signing her husband's name...the last signature of the last name is identical to the signature on our lease. Meanwhile, she has charged us a late fee of $85, and that plus the $150 money order, plus the $35 fee to cancel the check, plus the $15 fee for tracing the money order means $285 that this has cost us, plus the stress between my wife and I. Is what she did illegal, and if so how should I handle it? Should I get an attorney and go the claims route?