The essential decisions with Mac laptops these days are:
- physical size (13", 15", etc.)
- amount of RAM (typically the limiting factor in upgrading to newer OS versions)
- amount of SSD (or HD, but Apple is rapidly phasing out spinning disks)

My advice: minimum 8GB of RAM and minimum 256GB of SSD. Double both to get some headroom for the future.

On the list of things that she uses her computer for, you notably did not include photo management; hauling around videos, BitTorrented or otherwise; having a huge library of music; etc. If she's using any of that stuff, then you really want to spend the extra bucks for 1TB storage. Not cheap, but far more future-proof.

(Incidentally, the 11" MacBook Air is a lovely little machine. I personally have the 13" MacBook Air, mostly because I wanted the SD slot for digital camera things. I don't mind its light feature specs, since it's only for traveling. When I'm at home, I've got beefier hardware.)