Recently I had to take my girl to the vet as I was very concerned that she wasn't in season yet. She has always previously been every 6 months on the dot apart from when we got our pup and she skipped one. She has sometimes had a long prelude up to the season, which just means you have to keep an extra close eye. My vet is only just out of university, however she is very dedicated, really knows her stuff and I trust her, but when she said she thought that she was having a silent heat I was sceptical. We checked for urine infections as they can be a real problem, and I suggest you do the same. To be on the safe side I am treating my girl exactly as I would if she was in season, i.e. not walking her in crowded public spaces, not going to the local dog walking trails, and keeping her away from intact males especially.