She is wanting a mid-zoom faster lens.
Then get her one of those. What is mid-zoom, I don't know. 50 mm 1.4? How about a 35 mm Sigma or the 30 mm crop version (what ever it is called)? Your idea, 85 1.8, is not that bad either. It's a very fast focusing lens. The 135 mm 2.0 is also great, but it is not that versatile.
The suggested macro if definitely nice too, but how is it a fast lens or mid-zoom?