The problem MAY be due to lack of calcium. The eggs could be thin-shelled so they were easily broken. Separate the pair and give the hen the calcium she needs for tougher eggs. You can grind oyster shell, cuttlefish bone, etc..For no reason at all, I don't like calcium tablets ;D
Sunlight will also help in the absorption of calcium. I use fine siffted sand in the nest bowl. This will aid in cushioning the eggs.
Good luck.