Not defending her but a couple of thoughts:
If only one is on the lease, it would explain her not being let in Friday by management and her not having keys. If he was the income, both things make sense, they would be careful about that, people break up, there is liability, etc. In some complexes, keys are only given to the adults on the lease and if you want an extra, say for an adult child to check on your place while gone, you pay quite a high price for it.
I would also say it is not unusual to not take things like house keys on a trip if someone else is going to be home with the children.
Finally, it could certainly be a lie.