"Just fine" is relative. I'm a spatial analyst professional and that setup would make my head hurt. In fact I cringe just thinking about it, I simply couldn't do it. At the very least she should use Boot Camp and run ArcGIS natively.
But having been in the industry a while I know that there's a big range of users and applications of GIS from the very light to the power. Many people only want to plot a small amount of vector data they've collected (points/lines/polygons) coupled with some boundary data from the internet to make some very simple maps, or do some very simple geoprocessing operations like buffer, union, spatial join or update coupled with some simple reporting. For these uses a MacBook Air or even this rMB would be OK.
Then there are power users that work with very large volumes of data and images (in the gigabytes or even terabytes) and develop sophisticated spatial models for research and development, running analyses that can take hours or even days. In no way can an ultrabook fulfill these needs.
Simply saying you use a professional software and implying it runs fine in all situations or that it means the hardware is a capable professional machine is misleading. It's a bit like saying you use Photoshop when all you ever do is use it to rescale or rotate images. I have a pretty low tolerance for waiting though, especially UI sluggishness.
My mid 2015 rMBP Pro runs ArcGIS (and SPSS or any professional software for that matter) brilliantly and I often have these two packages running and using 100% of CPU and RAM, sometimes for short periods (under a minute) and sometimes for much longer. This MacBook would have a panic attack trying to do complex operations on large volumes of data.
So really just fine is relative. Yes you can get away with it for simple things, but the hardware is a very limiting factor when you need to do more.
It's not a professional laptop though and I think it's good for a lot of things in the light use realm.
