I'm a tad concerned that spider keeps coming back for more on this thread? That suggests either troll activity or an unawareness of how much you are riling folk with a situation perceived to be quite worrying for the animal involved. I'm also wondering, in a very well meant way, if the OP is not quite with it or doesn't feel capable of arguing or explaining her point of view enough. I apologise if this isn't the case.
I hope everything works out if this little shettie is pregnant. I do think it would have been a good idea to have a vet visit when you first rescued this little pony so as to establish her health situation but thats just because I'm inexperienced and its what I would do for peace of mind. After all, its not just the welfare of this pony you have to consider. Having another horse, the risk of infection and the financial implications of dealing with any problems will have a knock on effect on the care of your existing animals. I always love the idea of saving some poor little tyke, but I know that my number one priority is my existing horse.
Anyway, I digress. Being an OP you always risk your opinion being disagreed with, and people can get quite passionate about their views. When these opinions are disagreed with, and justification doesn't seem feasible, or if this advice appears to be ignored, it can feel quite frustrating for those offering the advice and help. I think some of the responses on here come from passionate people who care about the pony at the heart of this.
I've done a lot of things wrong with my horse, I've reasoned in my head that these things were ok...at the time. Looking back, I acknowledge the problems I caused and would act differently now. Unfortunately as humans, we learn best from our own mistakes. Be careful with your shettie's situation, I do worry that your insurance won't cover as if they know that there was a history of something, they generally exclude it - heck mine retrospectively excluded mites because I had been informed that there was risk of getting them reported in my vetting cert from purchase. I would hate for this to end badly.