The vet came out today and confirmed what I suspected. Consuelo is not pregnant, just overweight, with all the fat concentrated in her belly. So I lost 5 months when I could have been getting her into shape, which really has me bummed. Not to mention all those dreams of a little broom tail foal to coddle. Not to mention that in order to rescue her from extreme neglect, I paid almost double for a "pregnant" mare. I thought I would be rescuing two at the same time. I will be hiring a trainer to help me with ground training, and looking for a used cart next year. Fortunately, she seems happy enough with the sheep and my very large dog, and shows no need for other equine companionship. I fostered a large pony last year who pined for another horse, and it was sad to watch.
OK my pity party is over and done with. She is otherwise healthy and has a very sweet and gentle personality. The vet approved of my leaving her loose on my 14 acre fenced farm so she has some free agency. We expect that once she begins to get some regular exercise, and she is no longer on pregnant mare rations, she will begin to drop the weight. Yesterday she had a case of pony zoomies, scattering the sheep and racing about for a good 20 minutes.
Thanks to those of you who gave me good advice and encouragement. Now I can delete all of those pony vulva and udder pictures from my camera, and maybe get a little more sleep.