Early entry makes sense if you feel like she is ready for the social/emotional aspects; the cutoff will be at best a rounding error by the time high school/college rolls around.
Looking at your past posts, your kid tested very well on the IQ testing. I don't know that I'd use a hard line for this choice but certainly for anything over +2SD (i.e. 130) I would strongly consider early entry for a child close to the line.
My now 5 yo started kindergarten this year at 4 yo with a September birthday. He's got some asynchrony issues (socially/emotionally he's a bit behind combined with being the youngest in the class), but I cannot imagine redshirting him. He's academically so far ahead that I would imagine that him being the oldest would just result in more problems because of boredom.
Two additional thoughts: as I understand it, Louisiana makes acceleration pretty difficult after first entry, so I personally would take the early entry even if I know it would be difficult for a while.
Second,
http://www.newyorker.com/tech/elements/youngest-kid-smartest-kid It's not that there won't be problems, but that part of growing up is learning to overcome challenges through working hard, self understanding, etc. Shades of the growth mindset and all.
