How is it possible that when time runs out on the iPad, there is still time on my daughter's iPhone

If it were me, I'd turn off Screentime on all of her devices, remove all the content restrictions. Then, I'd make sure that all the devices were updated to the most up-to-date version of the system software they support. Restart everything and then set up Screen Time again.

What do you mean by "when time runs out?"

So you're talking about Screen Time? Are both devices using the same Apple ID? Do you have Settings>Screen Time>Share Across Devices enabled?