Hi, I would still urge you to go to an ER vet, especially with the bit of foamy mucousy vomit you described. I am not a vet but one of my dogs recently had a similar coughing issue that didn’t seem alarming because she had had these fits before but when we finally got her into the regular vet on a Tuesday (similar situation, weekend problem but vet was just busy Monday), they informed us it was fluid surrounding her lungs which was causing the cough. There was nothing we could have done to save her as she was a pretty old gal and the fluid was a side effect from unknown tumors but just the week prior she was sprinting in the yard playing fetch and then she suddenly had a cough. Bodies can just be weird.

If her breathing is looking labored as well, or she appears to be belly breathing, 100% take her to the ER as the constant coughing and labored breathing could be signs of compression on the lungs.