Dishonest Co-Worker

Completely not ttc related but there's nothing more that I hate than dishonest people. Everytime I go on vacation or have a day off I have to watch my back. I just saw an email from 1 co worker about all the leases she got (I lease apts for a living) so I email her saying "Nice! Good job!". She emails back saying thanks & that 1 is a split. I ask her who it was and when she tells me the name I said that our manager emailed earlier & said she left a vm saying she was ready to lease. The rule is if you your them first the lease is yours. I toured them in March and have been dealing with them since. Why should I give up 1/2 of my hard work just because they decided to come in when I was on vacation?! She always does this when she can't get away with stealing & when I catch her trying to steal a lease she then says we will split. I absolutely despise dishonest people!! It completely gets under my skin. Urgh... Sorry I had to vent. I'm always honest & my kindness is taken for weakness. I wish I could just quit. It's been almost 4 years of having to defend myself. I'm so upset & sad.