Well I have to say, it is better to "have" the money (as long as the check is good on the 14th) ahead of time, but I would def worry a touch, just reinforce the importance of payment on time, and dont EVER waiver on your contract, maybe everything will be just fine. I would def inform her that the check does need to be marked for the date of payment due next time and the money needs to be available, maybe she is having a hard time getting back to work? Post dating a check is pretty much the same as paying late! which I'm sure is against your policy, just wouldnt let her do it again. good luck with the new venture.