Skin problems in dogs are usually related to allergies. They can get secondary bacterial and yeast infections. Unfortunately there is no way to know if Minnie has a yeast infection just by looking at the a picture. I would recommend taking her to a veterinarian where they can do a thorough exam and skin cytology. They place a slide against the irritated skin and then stain the slide and examine under a microscope. They can then give medication based on it is bacterial or yeast. If the primary areas are the armpits and the belly- I suspect that Minnie is allergic to something in the air which has caused a secondary infection. One thing to remember with allergies is that there is not one magic treatment . Do not get frustrated when the first treatment doesn't' work, each dog is different. Allergies can be controlled, but not cured. Thank you for reaching out to Petco Pet Education Center, formerly Petcoach!