Skip the 4S. Out of the box it's 2 years old now. (If Apple's trends continue) It will see an update to iOS 8 late next fall, then fall off the update wagon. iOS 8 on the 4S will be slimmed down and not be likely to have all the new features. There is a slim chance though Apple bumps the 4S off the support wagon with the current release.

The 5/5c will see major OS upgrades likely out to iOS 9 in late 2015, or the 5s out to iOS 10 in late 2016.

As for the 5/5c vs the 5s. it depends on her use case. Does she like to take photos? If so, the added 10fps burst mode and auto "good" photo selection of the 5s may appeal to her. As would the more natural lighting flash on the 5s. I'll be helping a family member jump from the 4S to the 5s here soon solely based on the camera improvements.

Storage wise, keep in mind that you can have less on the device if iTunes Match is used. All of Elaine's music would live in the cloud, and could be played anywhere she has a data connection. And Music can be pulled down from Match and cached locally on the device. This service is an extra ($/€)24.99 a year.