Since it calls out your BAB, I'd rule that it only counts your level based itterative attacks. I've had people try to get insanely powerful Deadshots by holding another firearm in their off hand and saying "Well, in a full attack I have all the potential shots from my off hand firearm, so that should be counted towards my Deadshot". Yeah...no.
My rational is based largely off of this line:
"...but makes as many attack rolls as she can, based on her base attack bonus."
It's not "as many attacks as she could potentially make with a full attack", but as many attacks as her BAB would normally allow, not looking at potential modifications to the number of attacks. It's an ability meant to offset the fact that you can't normally make iterative attacks with firearms due to reload times (hence why you get it one level after you get your first iterative attack), though it's made obsolete by the fact that it's easy to reduce reloading firearms down to free actions, namely Rapid Reload + Alchemical Cartridges.