A lot of finding the right shorts is trial and error. When I first started I got PI (Pearl Izumi) shorts, but have since found that nothing PI makes actually fits me well. Their chamois' are too thick and actually cause my legs to go numb on long rides. Since then I have learned to read reviews - the ones here at TE for the products they sell are usually very good and spot on from the buyers.

Through all my trial and error I have found that my first preference for shorts is Castelli - their chamois is perfect for me. But they are super expensive and I haven't noticed an overall quality difference in their shorts versus my second favorite - Louis Garneau. I like thin chamois' that are barely there and I need fabrics that wick like crazy (super hot here and when I ride in Houston, super humid). Jerseys from these companies are another story completely. A third brand I have recently tried is Primal - I like their stuff a lot, especially their jerseys, and the shorts were great, but they don't breathe as well as I'd like.

Really the secret is to find what you prefer by experimenting. Lots of ladies on here sell gently used shorts for a lot less than the MSRP, you could always start there.