Hello,
This is Dr. Christian. Welcome to JustAnswer. How far into the pregnancy is she? Do you see any blood in the discharge? Does she seem distressed or ill in any way?
The discharge at this point is probably completely normal at this point, based on what you've described. There is no set time frame with some of these things. You'll know the true start of labor when she starts nesting and then of course pushing. Smaller cats can have a little more difficulty and so watching her is definitely a possibility but it won't happen over the course of 15 minutes but more like hours. For now it's okay to continue to monitor her. If she has not had her kittens in a couple of days then have her checked by your vet. Here's some links that might help:
http://www.petplace.com/cats/normal-labor-and-delivery-in-the-cat/page1.aspx
http://www.petplace.com/cats/dystocia-difficult-birth-in-cats/page1.aspx
Cat Veterinarian
12 year of veterinary experience in feline surgery, medicine and behavior