I am so sorry for your loss, it is devastating to lose a foal.
Originally Posted by Chiilaa
It depends on the type of twins. If she had fraternal twins, then yes, she has a higher chance of producing twins again. If they were identical twins, then she has the same chance as any other mare to have twins, regardless of having had them before.
Twins in horses are always fraternal, but yes she would be at risk of twinning again. The reason that twins don't work in mares in because of the type of placenta horses have. The entire placenta attaches to the uterine wall (except at the cervix) so when there are two babies in there neither placenta gets to attach properly so both babies are oxygen deprived and both have partial placental detachment.