
Your other bitch no doubt
was in season for the usual 3 weeks, but was one of the ones where the discharge became pale when she entered her fertile time. Your new bitch sounds like one of mine, who bled continually for the full season. Her last litter was born after matings on days 18 and 20 of the season.
Give her a good wash, as well as all her bedding, and wait another few days to be on the safe side before you let her loose with a male dog.