How Should I Charge My Client for 3-4 Hour Drop-In? Please help!?

I need help, please!

I have a regular who books half-hour "walks" for her dog 3 days a week. Recently, she asked if I'd be willing to stay with him 3-4 hours a day, 3 days a week. So 9-12 hours total a week. I say "walks" because her dog is incredibly anxious, so it's difficult to even get him outside to use the bathroom. I take him out to the bathroom and as soon as he's done he's pulling to go back upstairs. The owner asks me to stay with him for the remaining half an hour. This dog is also basically my weight. They also do not have a backyard where I can just let him out to go. We live in NYC and they live on the 5th floor, and he does not like going downstairs or in the elevator.

I offered to reactivate the drop-in visits service for her to book. The problem is that she only wants to pay about $25 each day. So I'd only be making $75 for 9-12 hours of my time that could be used to walk other dogs and make more money.

For one half-hour walk I make $16 alone (a walk is $20, but Rover takes 20%), and the minimum wage in my area is $15 an hour. I really like this owner and her dog, but I feel as if $25 for 3-4 hours is not an appropriate price considering I could be making more somewhere else, I could be using all that time to walk other dogs, and 3-4 hours is just a lot of freaking time to commit to a single client!

Most drop-ins are booked for half an hour to an hour, and people in my area are paying $25 for just that time alone. The time I'd be committing to this one client drop-in alone would be 4x that.

So how do I price this, and discuss it in a way where I don't seem like I am trying to just get money out of her? She seems to be set on or very close to $25.

Is this unfair? Or am I the one in the wrong? She had another girl who offered to do it for $25 a day, but the owner has stated that she'd really like to keep me because of how well I do with her dog (he is not an easy dog to deal with)

Thanks so much in advance!