What If I Recieved A Demand For Rent Or Possession Notice In Colorado And My Landlord Has Changed The Terms Of Our Lease?

I am 2 weeks late paying rent on my rental house and my landlord put a demand for rent or possession form on my door. In the demand she is asking for a $200 dollar late fee when it states in my lease its only $50. She is asking for a pet deposit even though im aloud to have 1 dog and 1 cat and it says no were on the lease that i have to pay a pet deposit. It says i have 3 days to pay it or move out. How can they legally do this? Please help!