How likely is HSV-1 Transfer?

I get cold sores on occasion. Last night I performed oral sex on my gf (briefly, like 40 seconds, not that it matters I'm sure) before going to regular sex. I woke up this morning and realized that I'm developing a cold sore. Or at least I think I am there is a small bump, not blister yet though. I know that she is at risk for transfer, but is it pretty much a gurantee that it was transfered to her genitalia? Or is it a 50-50 shot? I'm kind of ignorant on this.