<human>: This has been an ongoing mystery for us. We first thought our shepherd mix puppy was in heat roughly around 6 months because my wife thought she looked swollen down there. We did not see any discharge or blood, but she (the dog) also is pretty fastidious about licking and cleaning herself. We live next to a male 3 year old Dalmatian, but he never seemed interested in her during that time, which seemed to suggest to me that she wasn't actually in heat. 

Last week (she is now a little over 8 months), we thought we saw some dried blood on the outside of the vulva. She did not appear swollen. Yesterday, a different (fixed) male that we run into frequently who previously ignored her was suddenly very interested in her, which the owner remarked as unusual for him. As far as I can tell, there is no white discharge and no blood, nor does the vulva appear swollen. 

I don't want puppies and our training class asks that we don't bring a female in heat, but I can't figure out if she actually is or ever was in heat. So is there any indisputable way to figure out if she is in heat? And to the German Shepherd/mix owners out there, when did your female enter her first heat?
Note: She will be fixed around one year of age. We were told by our vet that it's best to wait, if possible, until they stop growing to fix, especially in the larger dogs.

Could you distill the essence of the text into 1-3 sentences?
<bot>: Can't tell if my 8 month shepherd mix is in heat, but displayed the occasional sign over a 2 month period. How do I tell if she is in heat?