Golite? Enlightened Equipment (quilts though)? Sierra Trading Post + good coupon--various different brands and temp ratings?
Dunno, there's plenty out there that are below 300 for summer temps and ratings. I think the Golite bags are pretty good for the price. If she is open to using a quilt, i would say can't get much better for the price with an Enlightened Equipment quilt. Quilts are really so much better for the summer anyways.
I just got a E.E. 40 degree down quilt (the Revelation X "model"), slim and short style (for 5' 6" height). With the straps that come with it, it weighs a total of about 15.75 oz, very packable, uses 850 fp down, and only cost 175 (plus 10 dollars shipping).
Very well made, very nice overall quality, and i'm very impressed. I was going to take it out this weekend, but my wife pulled the wife card & said i needed to do house/yard stuff, etc.
Good luck with your search