Has my dog got taste for blood?

our bullmastiff is 3 and has always been gud with other dogs and a while ago whilst out walkin she attacked a small dog badly and out of the blue and for no reason since then she has attacked another dog but it was in her terrotry that time but she did go over board and wouldnt stop bitin at the dogs leg and shakin it, it was really horrible!, now she has had an op on her leg and she keeps likin and bitin at it and has even gone as far as gettin the dressin off it and eatin it durin the night and then makin her leg bleed!, i really need to no if she has a taste for blood, i am 6 mths pregant and cant poss have her round my baby if this is the case , i hope it isnt but i need to no as she has also started to bark visiously at people walkin by which she never did before either, i really dnt no whats wrong with her but her personality over the past yr has really changed!... if anyone has any advice i wud be really grateful ...thank u