I'd wait since she's so close to delivery, and you want to worm her within 24 hours of delivery, as it can help with foals scours during the time momma goes into her foal heat. Many people find the immediate worming very helpful in keeping baby from getting such severe diarrhea during momma's first heat cycle and it is safe for baby, so no worries.
The waiting is the hardest part of this, but keep a good eye on her, as you want to be there to help her if you're needed. As soon as the little one arrives, you'll forget how tired the waiting has been. Hang in there, she's coming along just fine.