My 15 month old bitch has started her first heat, she's swollen, but no blood, just a watery discharge. I haven't seen this before, blood is considered the first day. Should I give this more time or have her checked?

I'd have her checked. Last fall I missed a heat somehow even though I was checking daily. The bitch had watery discharge, when checked, her progesterone was 20 something. We tried a breeding to my own male and missed. Her mom was super hard to catch in heat. I'd run your girl in just to get the vet's opinion.