She may have had what my vet explained to me as a "silent heat". He says sometimes the first heat is so little, you don't even notice it. I would not be concerned with it. My Yuna is having what I thought was her first heat at a year and a month old, and he told me that was not likely, and that I missed the 'silent' heat because she did not bleed much or not at all. I don't know if this is the case, but he sounded very confident about it.
I also moved this topic to "Your Bulldogs Health" so others can find it easily in the future.