It really comes down to how tech savvy is she and how patient can she be when it comes to waiting for bug fixes.
Android, as you know, is a phone OS with a learning curve. it's not like iOS where you pretty much just pick up and go. With that being said, I've always been an android person and prefer it over any of the other smartphone OSes out there, but I'm also a very tech-savvy person. ICS is without a doubt the easiest version of Android to learn (IMO) and if she really likes it then she should go for it.
The Nexus is a great phone, but it's also important to remember that it's not without flaws. Granted, most of them, if not all of them, will be fixed with updates in the coming months, but they are issues you will have to live with until then. Personally I haven't had any serious issues with my GNex. It reboots itself occasionally, the battery is easily drained if you are consistently on it, and the cell phone service display is always showing less than stellar service (however I have never dropped a call and never have any issues making or receiving a call, even with 0 bars). It is important to understand this before you make your decision. But it's a brand new phone with a brand new OS, there are always flaws in that situation.
It really is a great phone, and even with the minor issues it has I wouldnt trade it for another phone on the market. I would just hate to see you (or her) dive head first into the purchase only to be disappointed a few weeks later because you were expecting a perfect phone.