I have just gone from the 4S to the 5S.

Certainly the 5S is a great phone and I love it. For my uses I'm not sure the extra speed and memory gets used that much. I use it for TomTom and email mainly. But even as a non-power iPhone user I still think the stretch to the 5S would be worth it.

The finger print unlock seems like a gimmick until you have used it for a while. Now every time I pick up a device I get annoyed when it does't unlock with my finger print. It is one of those nice features that isn't all singing and dancing but is really really nice and even works too !!!

The camera is much better, the super slomo 120fps 720p video is actually really amazing. The flash has been improved a lot with this version. It's still a camera phone of course, but a very nice one.

So even as a regular user I would suggest the 5S would be a better option, unless she loves bright colours and plastic in which case go for the 5C but as others have pointed out the price difference isn't all that.

Cheers

Cris