Her being on fescue does not mean that the foal will be dead. It just means if the fescue is infested with the endophyte fungus that there could be complications with the pregnancy. The complications could be prolonged gestation, abortion, thickened placenta, retained placenta, or suppression of lactation. Only one of these possible problems will kill the foal out right and I know that she has milk. So, we can already rule out one of them.
If she is pregnant then there are some drugs available to counter the effects of the fungus, so I would put her on one. I would also move her to a dry lot and buy guaranteed non-fescue hay. Most grass hay in this area has some amount of fescue in it. So, I may end up buying chopped timothy from the feed store until I find a better source.
Anyway, I moved my appointment with the vet up to tomorrow afternoon. I will know for sure then.