Lea,
You've gotten very good advice. I wouldn't recommend mating your bunny since she's already a year old. I'd hate to see you lose her, which would be a possibility at her age. Not only can you have dead babies (pencil kits if they are pushed through too small of an opening), but the mom can die from complications at birth. As Pam suggested, the babies can become stuck because the opening is not large enough for them to safely pass through. If this happens, you may lose her if you don't get them out of there safely and in a timely fashion. There are all kinds of horror stories about this happening, especially with Hollands since they are such a small breed.
If you are interested in breeding, I'd look to get another female that is younger. Breed her when she is closer to 6 months of age. It will be much safer and you won't be putting your beloved pet at risk.
Dyan