This is natural herd behavior for horses. The reason she is so "herd sweet" is because she doesn't feel safe with you. Plain and simple. It's not something we want to hear, but it's something we NEED to hear. My horse used to be herd sweet as well, but not anymore. I've worked through that issue with him using Parelli and it's worked wonders.
Basically she is telling you she doesn't want to be with you. The things that are important to horses are safety, comfort, play, and food. They usually go in that order. If you're my horse, food is now number one lol. The herd provides that safety, comfort and play, and we need to do the same so that the horse will choose us over other horses. This takes love, language, and leadership.
This is a very complex issue to write about over the Internet, so I would suggest looking into the Parelli Seven Games. That will not only build trust, but also rapport, respect, and a language that is more natural to the horse. You can go to www.parelli.com
and get the Free DVD, or order the Seven Games DVD they have available.