At this age, I would switch to adult food, a grain free food with a red meat base from roast's not meal. For instance, beef, bison or venison. Fromm Beef Fritata, or Taste of the Wild Prairie check the food ratings here on EBN and then Pet Flow will have all those foods and the ingredients. I started all my bully's on adult food at 5 to 6 months old. three times a day, at a year old two times a day. If your pup is undersized, give a little more.
sherry has it pretty well covered. there are kibbles that have higher protein or were you going to cook something. boiled chicken and lowfat hamburger may help with the kibble. there are canned food used as topper to help. yes raw is another road. i feed mine grandma lucys freeze dried with my kibble. if you just up how much you are feeding as long as tummy is ok that should help to.
add green tripe to her feed it will bulk her out,but given genetics she may be a petite bulldog ,not all bulldogs a big and bulky ,she will fill out shes still a baby and has plenty of time ,karen