One of my hens had almost the same thing (except no foaming at the beak). She was wheezing too. Sounded like something was stuck in her throat. I made the mistake of grabbing her to try to massage her throat and crop, but just caused her major trauma by making her panic and breathe even harder and struggle. Her comb turned purple and she was croaking/gasping like you wouldn't believe. I thought she was going to drop dead right then. But when we put her on the floor of the coop and left her alone, she was fine the next morning. I would never have believed it.
So whatever it is, if she's having trouble breathing, make sure she stays CALM.