
Sounds like a Split season.
Some bitches will start the season, but then the hormone levels are not high enough to continue the process and everything stops only for them to come in properly about a month later. I tend to call that a false start as the later season is a full length one and they ovulate about the end of second week.
Keep an eye out for any sign of ill health or an unpleasant smell to the discharge, excessive drinking etc.
Pyometra (womb infection that can cause blood poisoning and eventual death) is rare with a first season, but has been known.