A Girl and her Mule(?)

I recently acquired a large collection of vintage photographs from an estate sale.  The photos date from the 1920's and 30's, so I'm assuming they were not taken by the person whose estate sale it was, but perhaps a parent or other relative.  From reading through them, it appears this person may have been a nurse and the photos are of many different people, perhaps friends and work acquaintances. Most were taken either in Cape Girardeau or St. Louis, Missouri.  The nice thing is, many are labeled with the name of the person in the photo and the date the photo was taken, a very uncommon practice from my own experience with vintage photos.  I plan on posting some of the more interesting ones over the upcoming weeks.  I also plan on attempting to locate relatives of the individuals in the photos to return the pictures or at least provide a scan for them.

Of course, having said that about the labeling of the photos, the first image I offer up has nothing on the back.  Just a girl and her mule(?).  I question that, because honestly, I'm not sure if it's a mule or a horse.  Initially, it looks like a horse, but then the ears look a little large and the mane seems a little tight.  Maybe someone with more horse/mule familiarity can clarify.

The shadowed line in the photo isn't a crease or a shadow on the scan, but rather appears to be a defect in the film.

I'd place this photo in the 1940's given the pants the girl is wearing. I believe these were called "Sailor's Pants".