1. The girl back tattoo has been so popular that in many circles it is now seen as very unoriginal. Unfortunately the low center back placement has been heavily played out. Many girls have followed the trend, and hence it has become more of a fad than an original idea for placement.
2. Slang terms such as "tramp stamp" have now developed which refers to females who have a girl back tattoo in the low-center area. Some have said in 40 years that slang term will be replaced by "gramp stamp" playing on the notion that the plethora of elderly women who will still have the permanent girl back tattoo art in their later years. The popularity and common placement of the low center of back tattoo lends itself to this type of slang creation.
3. Finally, and the most obvious danger of getting a low center girl back tattoo, is the fact that you are unable to visually see your tattoo, unless you look in a mirror. This is of course the case with all back tattoo's, and if one would like to view their body art frequently, without a mirror, they should consider placement elsewhere.
If one is dead set on getting a girl back tattoo, feels the placement is right for her, and can rise above the slang terminology and such, then it would be a sound decision to proceed ahead with the lower center back placement. Otherwise other placement options should be explored.