It really depends on your use case. I've heard quite a bit positive feedback about elementary OS for "computer illiterate" (parents, old people, etc). It seems to "just work" for them after installation (bear with me I really can't judge about "ease of use" after years with Linux) and it's running on Ubuntu LTS versions. You're running apt-get to install security fixes, the current version of Firefox/Chrome and fixes provided by the elementary OS team, and that's basically it.
Fedora on the other hand is "the latest hot thing". It has by far the best GNOME3 integration and it previews technical features worked on by Red Hat and GNOME. It also features recent kernel versions which might be important for new-ish hardware. All that is quite awesome for technical-minded people like me. I'd like to say "it's unstable", but in my experience, it's not. I did not do the 22 -> 23 transition yet though. You have to do some additional work for the frequent new versions (backup everything in case it breaks, try the transition, etc). You also have to fiddle around with GNOME addons, font rendering and media codecs (RPMFusion as third-party provider) to make it usable as "personal computer" IMHO.
In the end it's up to you. I do believe your mom will be able to work with both (you'll need to tweak GNOME a bit IMHO, but that's up to discussion I guess), but you'll have to deal with different administrative workloads.