Yes, perfectly normal. Here's a site that gives some technical info, but basically every bitch and every season may be different. The season can last as long as 30 days, although there is usually no discharge after about ten - 12 days. Some bitches don't seem to have any discharge at all, while others drip all over the floor. Best advice is to keep her away from males for at least four weeks, and if you are thinking of having her spayed then the best time is about three months after her season.