
That sounds like old blood that just needed to come away, it may have been trapped high up in her vagina and some exertion has dislodged it, this can happen to us humans too when we think things are done we get some stale blood passed, better out as it can't then become infected.
Watch her temp and give her a good sniff a couple of times a day and at the first hint of change get her to the vets for A/B's.