J.O.
It certainly sounds like it's vaginal. When we have bowel movements we use the same muscles that expel cervical fluids. Is it possible that she is ovulating now? Some women see blood like this when they ovulate. This would fit (depending on her cycles) with the timing from her last period. Is it possible that she is pregnant? Some women see 'spotting' similar to a period when the fertilized egg implants.
Another possibility is that she has tears in her bladder. I have this and, as a result, always have blood in my urine. The problem with this is that it can only be diagnosed when everything else is ruled out. (Although, if she is sure it's not in her urine, this wouldn't be a consideration.)
Since she is fairly certain it's vaginal, her obgyn is probably her best bet.