Reliable advice can only be given (and taken) if you first say what your needs are?
Exactly! One of the reasons I got 13" Retina is the resolution compared to other 13" laptops that mostly offer up to 1366x768. 11" Air is 1280x800, but 13" is 1440x900 so it is better for me already.
However, I always look for as much screen estate I can have (however funny it may sound when talking about 13" and 11" laptops

), but it is, again a matter of personal preference and I bet most normal users don't really care much about it at all.
The question is what are you or your gf going to be using the computer for.
I think Retina is kind of a tricky issue, and certianly it is not for everyone (as in computers and bigger screens in general) at least in my humble opinion.
Second thing, I am no expert, but from what I read (on MacRumours as well

) the Macbook update is just around the corner (with the WWDC happening), so maybe it is good to wait just a little longer and do a research after the "refresh" or whatever they will announce then, it's not even a month of waiting

.
I am not sure if Apple is going to even announce rMBA as for now as well, though.