Yes, usually, the most likely scenario is what ends up been the problem -in this case, bacterial infection. She'll be just fine with the antibiotic.
The concern about bacteria growing on wet food left outside is common. Personally, I think it's bunk. For one thing, if this bacteria was so bad, the human race would have died off thousands of years ago as refrigerators are, historically speaking, something that was invented yesterday. I mean, the reason why spices were so appreciated in medieval times was because they masked the flavor of meat that had began to go bad! For another, birds in the wild are exposed to all kinds of bacteria all the time -even the bacteria that causes rotting (a process that people associate with yuckiness but which, in reality, at the beginning, is nothing but fermentation (which is a VERY good thing precisely because of all the good bacteria it creates!). So much so that there are parrots that choose fruit that is already rotten on purpose (the 'drunk' parrots of Australia). Bacteria has become a synonym of something bad but not all bacteria is bad and, even bad bacteria is necessary for a healthy immune system.
Personally speaking, I've been feeding gloop for 20 years and have never had a single bird come down with a fungal infection and very, very few with a bacterial one -and then, even these bacterial ones couldn't have been caused by the gloop because, if that was the case, all the birds would have come down with it at the same time (food poisoning) and not just an isolated case once in a blue moon.
I would think that Ocean's problem is extra stress due to Tanya's joining the household...