At 3 1/2 year old, I doubt she got bred. It's often very difficult to get a doe bred who hasn't been before 1 year old. If she did get bred, I would be more concerned with her kits not making it than her having trouble, but would still recommend reading up on rabbit birthing and potential problems anyway, just to be on the safe side. That way if she is bred and something goes wrong, you'll know what to do.
You could try palpating her 10-12 days from the day you returned the buck to his cage to see if she's bred. Otherwise, make sure she has nesting material/box at day 27 and keep an eye on her for nesting behavior (pulling fur, carrying hay/straw or whatnot around, digging, etc.)