Hi, I'm Dr. Heindel, I'm going to try to assist you with your issue.
Has your dog been on medications recently? I see she's been sick. I wonder if she's not having a drug reaction to some medication she's taken. Other options are infection, allergy (inhalant or food), autoimmune, mites or other ectoparasites, or an endocrine imbalance, such as hypothyroid.
She had antibiotics for an ear infection but finished the course at least two weeks ago.
Okay, so it's unlikely a drug reaction then. You still have the extensive list that I listed that could be the etiology for her skin condition. I'm sure you realize that it is impossible to know which of these are the cause of her present skin condition. A physical exam to classify the lesions, the distribution and the general appearance would narrow the scope. There truly is nothing that could substitute for the information gleaned from observing the lesions in person. Sounds like you've been down the road of expensive diagnostics recently, so I certainly understand your frustration. I would suggest getting Poppy in for an exam and decline diagnostics, ask your vet to go on his best medical suspicion and treat accordingly. That will likely mean an antibiotic, but possibly a medicated shampoo, ointment applied topically, a steroid and/or an antihistamine. I think it's very reasonable for you to set a financial limit and ask him/her to prioritize and work within it. Often we can resolve stuff, without finding a definitive diagnoses, by just treating empirically. Minimally, a medicated shampoo, more aggressively, an oral antibiotic. I understand your frustration ... however, you must realize that we can only speculate on the cause of her skin condition based on your description.
I wish you luck in clearing up Poppy's skin issue. For what it's worth, Bichon frise dogs often have recurring skin issues ... usually due to allergies, which can develop at any age.