The first registered miniature foal we had due (and only one for that year as well) did not make it and we almost lost the mare in the process. This was over 25 years ago when we first started breeding registered miniature horses and I still remember even today the hurt and disbelief that I felt on that day and for weeks to come. Since that terrible day, we have been blessed with many, many lovely foals, and sadly even with cameras, monitors, and someone being present at the farm 24/7, and being within 20 minutes drive of one of the top rated equine clinics in the nation if we have problems, we have lost mares and foals during the birthing process. The realization is that you can only do the very best you can in trying to ensure the foals arrive safely and regardless things will happen and foals will be lost and mares will be lost - it is unavoidable. With that, though, it is the minority of the time - I tend to use the 80-20 rule and it seems to apply in the miniature birth process -in about 20% of births - something happens that is outside the norm and then - the 80-20 rule applies again - of those 20% that do experience problems 80% are able to be corrected/resolved, sadly the other 20% are not- but it is a small minority of the time. I've also noted that it tends to run in cycles - One year we had 3 major issues in a row in the same week - the University Equine center knows us on a first name basis unfortunately and when they have a call notifying them that says a miniature horse is coming in at 2 in the morning from Circleville, OH - they know it is us. Another year out of 25 foals - we only experienced minor issues and had 25 live births.
We are currently in the middle of the height of our foaling season and every time I have a mare lay down to deliver, I say a silent prayer that all goes well and if things do not, for help from above to guide me in making the right decisions to do the very best possible.
I'm very sorry about the loss of your filly and hope the above information from our experiences over the years is helpful. Don't give up - for you will truly have many lovely healthy foals in the future.