I had the same questions and concerns not too long ago.
Missy was 11mo old and I assumed she must of gone into heat and I missed it since I have heard it can go unnoticed. But at about 11 & 1/2 months old she went into heat and it was obvious. Her area down there will become very swollen and very noticable, her nipples may become enlarged too. There will be a lot of licking and more than likely noticable blood. The 1st week or so the blood was not noticable and she was able to clean herself really good.
But about the 2nd week the blood was so frequent I had to buy her panties to keep her area protected.
I think when she does go into heat you will know
good luck!