How do I proceed with pet care when O is not responding?

No response from the owner I'd provide dog food to keep the dog from starving

If you know the dog’s vet contact info, I’d contact the veterinary practice and ask if they stock that food and if it can be charged to owner’s account, or if they have sample trial size that can last two days, or what they suggest that you might have or be able to get (whether that’s dog food which you can give owner receipt at pick up and ask for reimbursement or human food safe for this dog).

For a dog with a diagnosed medical condition, some foods (including human foods generally regarded as canine safe for a healthy dog) are safer than others.

I too am dealing with a non-responsive client. It's incredibly frustrating. I am doing drop-in visits for her cat for 9 days. She said she would cover parking fees, but I needed to adjust the rate, and she needs to confirm. She has not not yet responded to any of my texts for the past couple of days. I can't just not care for her cat, and I can't afford to pay for the parking fees that are racking up. I wish I had heeded the warning signs that she is not a very communicative client when she first sent me the booking request. Her responses were sparse and not very detailed. I would have declined her request had I known she was going to be immature and uncommunicative throughout the booking.