Red sable is probably the best description. The mask and dark colored tail give it away. Sable can make dogs look pretty funky and it can vary a lot.
A few sable bulldogs for comparison
ONLINE PEDIGREES ::  :: ALL GAME'S KANNON
(This guy's sabling isn't as dark as your girl's, so he looks more fawn. He also has less of a mask.)
ONLINE PEDIGREES ::  :: ATILA'S DENDY (7xW)
(This boy has a bit more heavy sabling around his face. He also has the "widow's peak" on his head that's pretty common in sables.)
ONLINE PEDIGREES ::  :: <B>CANE VALLEY'S BABY GRACIE
(This pretty girl is a good example of the kind of sabling you see very often in the APBT
. To the untrained eye, she just looks like a red dog, in fact the ped says she's a 'red buckskin'. But, look at her back. Hopefully you notice the slightly darker shading on her back. This gives her away as a sable.)
ONLINE PEDIGREES ::  :: CANE VALLEY'S STACIE
(This is the daughter of the above dog. Like her mom, she's a very light sable. But look at her head, you can just barely make out a 'widow's peak' and her tail has a bit of black hair on it. This means that she's a sable.)
Sorry, I wasn't able to find any that looked much like your girl. Because they're often listed as the wrong color, it's ridiculously hard to find peds of APBTs of a certain color. However, your girl is most likely sable. Just darker than the dogs I found.