URGENT!!! Need answers for Late Rental Payment Penalty

Hi, I would like to ask for help regarding our problem with the penalty our landlady is imposing for paying the rental fee late. We first moved in last year last day of September but we did not get a contract. Because of hard times, we weren't able to pay on time last November but paid on December two times to cover the month before and for December. We weren't charged any late payment penalties that time either. However, we encountered another financial problem because I switched work just last month and I won't be able to get my salary not until March 15th. When the landlady got a hold of me, she told me that there would be a penalty charge now of 100PHP for every day we missed to pay the rental fee. So basically, our due date is on Feb29, however, since I will be getting my salary this March15th, I won't be able to pay her until then. Also, we were not given any contract that implies that kind of penalty. Is this even valid? We have the 2mos advance and 1 mo deposit with her. Please help us out!!!