If she has an iPhone then you really should look at an Apple watch. They just work. Never any issue with pairing, good range of finctionality, you don’t have to use all of it, nice interface and well designed, Basically, a typical Apple product. The Apple health stuff is slick and an Apple watch integrates with it perfectly every time.
An Apple watch would be the obvious answer as she has an iPhone but they have shit battery life.
Not sure what you expectation is of good. I charge mine every other night. If I use it heavily for mapping nd tracking etc then it will still easily last a day. Not sure why you need anything to last longer than 24hrs.