I agree with OakRidge, I would not breed a much bigger buck to such a small doe. The chances are that some of the babies will take after the sire and be larger than the others, causing the doe problems while kindling. A really big baby being birthed by a small doe is at risk of getting stuck and dieing. If it isn't removed, it will kill the doe as well, not to mention any other babies still unborn. Or it could seriously damage the doe, cause internal bleeding and again, you lose the doe... as well as the litter she can't raise.
The "responsible" part of proper breeding is selecting compatible animals to breed. Not just personality wise, but taking into consideration size, color, faults and breed standards.