What do I do to deal with this CRAZY customer, HELP?

So I am new to rover and I am trying my best to be excellent at customer service. Recently I house sat for a customer, when she booked me my rates were very low. Dog house sitting was 20 and cat sitting was 25. My rates were so cheap because I had no idea about pricing and I had not adjusted them to the correct rate yet. I've sinced learned dogs are harder and should cost more, my customer thought this too. With her three pets the total came out to be 65 a night on her end, not bad for me cleaning her yard, walking twice a day, sleeping with the dogs, checking for packages, doing trash and grooming their butts, right? Before we confirmed the booking she told me perhaps I should switch the prices to 25 for the dogs and 20 for the cat since she thought the cat was easier, this would mean I would earn a little more due to there being two dogs and one cat. At the time I didn't feel like going back to change the prices and I didn't mind giving her something more affordable. I told her we can just keep the prices the same, that she didn't have to pay more and if she likes the service if she would just leave me a good review. She agreed to this. That was before I knew how much of a task it would be! Now after days of texting her and keeping her calm I just finished my job. Whew thankgod it was over, or so I thought...tonight I got a message and call from her just as I'm getting ready for bed. I ignore the call seeing that it's late and I'm pooped. She asked if I can lower the cat fee she already paid for. I dont know if something got lost in communication but I'm nervous as hell because I don't want a bad review if I refuse her. I don't even know if I can refund her that money, but it would be a cost on me especially since I paid way too much in ubers getting to and fro her place. I've already given her a coupon for the future and a pack of bones with a ribbon as her early hanukkah gift and a thankyou note on top of everything. I feel used, I feel squeezed not to mention I'm a young woman of color trying to survive the city while she owns two boats and a grand piano but wants to pay me even less... how can I refuse this woman politely, proffesionaly in a customer friendly way so I dont get screwed?