I'll ask on facebook, see if any of my friends can recommend a brand.
This site has how to measure. I am not aware of the company, but should help you with what you need. Girth is important for fit, in fact most important
Her Girth is right at 22''. Ruffwear is what we have looked into, since they seam to be the leaders in dog packs in america. 22" is at the bottom end of the sizes of both the approach and palisades pack making them just a tad large for her. Although she hasn't tried on the XS approach just yet.
Another friend suggested these... I like the other better though: