How do you deal with a client that isn't responding?

Hey everyone...so here's the situation. A repeat client (2nd time) requested (about a month ago) that I watch her dog this Thursday. It's just for the day, not an overnight. I'm free that day so I said yes, and she paid and booked it. We didn't nail down times, as I figured I would confirm this as the day got closer. I now realize I should have confirmed the time frame at the time of the booking. It's now Monday and the stay is for this coming Thursday. Anyway, I reached out to the client 5 days ago and asked her what time frame she needs on Thurs. No response. I messaged her again yesterday morning. No response. I have another client (outside of Rover) who wants me for a few hours that same day, but the owner for this Thursday won't respond to me to nail down the time.

I hope nothing is wrong with the owner for this Thursday, but I'm not quite sure what to do. What do I do if she never responds to me? It's already paid for, but she never told me a time to arrive or leave. It's not like I can just guess and show up. It's unlike her to not respond at all. Thoughts?