How much work is expected in a "Doggy Day Care" situation?

I've recently started sitting a new dog who's fairly young, a rescue, and a service dog in-training. He's awesome - super chill, very lovey, listens to every command - and it's great. However, when I'm booked for him I'm being booked for most of the day (tomorrow is from 8am - 6pm). My standard rate for House Sitting is $30, though I gave her a discount rate of $25 for today and tomorrow, which in this case translates to $2.50 an hour. Normally I'm fine, since I usually play with them in the back yard, play with toys in the house, let them out for the restroom, etc.

However, this owner reiterates often how much she takes him out (hour walks 3x a day) and has requested trips to nearby parks during the day. On top of that, she has been constantly requesting pictures (which I've sent), but now it's more of "when he's outside". Well, when he's outside I'm busy with him! I a) feel like it's a lot to request these hours many days in a row with that amount of activity for a single dog and b) am beginning to resent the implication she doesn't think I'm playing with him by asking for more pictures.

Any advice on how to handle this tactfully? I'm a fairly meek person and abhor confrontation, but I also don't particularly enjoy the way this job is heading. I don't want to lose a regular client by balking at her demands, but I also don't want to be a pushover who works for next to nothing.