How long ago did she get in there? If recent, I would definitely abort. She needs to grow her body. If it was too long, aborting could do more damage than good.
Talk to your vet. I much prefer to abort if I know they are short bred... but you have to wait for about 2-3 weeks after the breeding so the lutalyse will affect the hormones and cause her to lose the pregnancy and then she will come back in heat..
It's like asking a 10-12 yr old to have a baby... her body might have matured enough to cycle, but her body is definitely not really ready to carry a pregnancy to full term. It has happened, to everyone that has had livestock... but it stunts the growth of the animal for the rest of it's life... and that is if you do not have complications with the birthing process.
If she is too far along, it can do more damage to abort her late term. And often will not breed again. Doing it early term, will basically "reset" her cycle... and will cause her to come back in heat again too...