It probably milk. If she hasn't recently had puppies then she could be having a phantom pregnancy. This is common in dogs and will pass in a few days. If its still coming out in a couple or three weeks or looks red, or swollen, take her to the vet.
My 10 month old chihuahua has two swollen nipples, I noticed them a couple days ago,they started by looking lumpy, then they grew bigger but didn't look lumpy, this morning I just happened to squeeze one (because I was trying to figure out why was it swollen) and a drop of a white liquid came out. I don't think she is pregnant, she's never around any dogs, she started her heat cycle in July, bleed for 3 weeks.
It's milk.. But that doesn't mean she's pregnant.
I'm assuming since you say "it's been 2.5 months" that a mating took place... Do you have an exact date? Canine gestation is a fairly specific thing, 62-63 days is pretty much on the money if only one mating took place. If you're actually at 70-75 days, then what you have is a false pregnancy... If you're not sure of your dates, but it's at least been close to 2 months, and she is pregnant, her belly should be very big and tight now and you should be able to feel the pups moving if you lay quietly with her for awhile.
If I am not mistaken she might have been bred in October; correct? If this is the case I would say that it is clearly a false pregnancy. However, if I am wrong in my first comment....you might just be a granny soon! Is it thicker than milk? If so, it could be Colestrum (sp.) which is what all mammals produce prior to obtaining milk.
That means she is going to be a mother