This is a congruent conflation of “fuming over (someone or something)” and “foaming at the mouth”, both meaning to be extraordinarily angry. The context makes sense: the speaker was trying to make a left turn against oncoming traffic and said, “”I’ll call you back in a minute. I’m fuming at the mouth trying to make this left turn”. “Running on fumes” also may be in the mix, as car fumes might certainly have been on her mind as well. A big thanks to Joseph Newcomer for sending this one in!