I'd wait for the next proper season as the foal heats job is to just get rid of any gunk left from when she foaled, the conception rate is also poor as their uterus is trying to sort itself out!
If it was very late in the covering season and you were desparate - then possibly, maybe, but as above, the mare has had quite a trauma to her body and she is sorting herself out internally.
I would wait this early in the season until her next.
So would I - particularly for AI. We find natural cover gives good results on the foal heat - but AI never as successful - not least because of timing. I had two due to be AI'd on foal heat today.
One was a visitor who owner's wanted on the foal heat for various reasons and as we were using the same stallion on my girl, it made sense. Yesterday they both looked good to be AI'd today - semen arrived safely this morning, but visitor had already ovulated on a 40 mm follicle!
And my own mare still had a bit of fluid (which we'll treat) but chances not great.