I understand your concerns because I was in a similar situation. I was going to London for treatment and I was really worried about getting a taxi there. Does your daughter have a phone and internet? I mean, the answer's pretty obvious, so no need to stress. You really should check out that article about ride-hailing apps in London -
https://blog.gettransfer.com/best-ride-hailing-apps-in-london-top-picks-comparisons-and-features/ . It's laid out nice and clear. The article compares all the possible services like Uber, Bolt, and others. It explains how to see the price ahead of time, the driver rating, pickup time and routes. I usually used Bolt 'cause it was cheaper, especially outside rush hour. But I kept all the apps installed and simply compared prices before the trip, like the article said to do.