..... do you put a nappy (diaper) on them?

We are only on day four of gentle potty training. We've been doing just underwear in the house and pull ups when we go out. Today, E stayed dry all morning, even though we were out and about, and even did one wee in a public toilet (in her little plastic potty). She did really well this afternoon at a play date (three potty wees and two accidents in her pull up). But her success is dependent on us prompting her to try every 15mins or so.

This evening, she was just so over it. I had her in underwear but she kept refusing to sit on the potty. Then, two minutes after she had tried (but no wee came), she weed all over the floor.

She has recently given up her last nap and is so tired by 5pm. Would you cut her some slack and put a pull up on her in the evenings? Or do you think that might cause confusion / bad habits? I am conscious that I don't want to turn her off the idea of using the potty by pushing it too hard when she says no...but I don't want to give the message that we wear pull ups when we don't feel like using the potty.....