Submission urination + snaping

My female dog when meeting other dog's submissivly rolls on her back and urinates. I understand I should not correct that but, when other Dog's go to smell her she snaps at them. And becomes dominant I do my best to correct the dominance with a pop up on the leash or a verbal command. This has happend at dog parks when I'm not close inuf to give the correction. Thats what Im worried about how do i socialize her when these incidents have potential to happen. Any advice? please help (She might be in heat) can't tell. I plan to get her spay after this cycle.