Taxis are perhaps the best form of transport - no jostling from other passengers - but only if they stick to the guidelines. My brother-in-law owns a taxi firm and I know that he insists on very strict sanitising of seats, door handles, etc, for each passenger, and passengers must sit in the back with windows open, and so on... However, we were in a car park recently and my DH, who used to drive for his brother's company, was watching a driver from another company. He pointed out that one lot of passengers got out, the driver handled their bags, and another lot got in. The driver didn't sanitise anything, not even a door handle, and didn't clean his own hands.
If you are going to use a taxi, you need to know it's clean. My DD used an Uber recently and said that the driver was careful to sanitise everything before allowing her to get in.
Is it the journey that worries your daughter or the appointment? If the latter, you are unfortunately unlikely to be allowed in. I understand that you want to go - so would I - but maybe it would be safer for someone younger to go with her. It just reduces the risk.