The bra band is the most important part when it comes to fit and support, and the lay of the underwire is a great fit indicator.
The bra shown above, for example is a poor fit. This is demonstrated by the distinct hollow visible below the center gore of the bra. You can see the shadow beneath the gore and this means that the underwire is not lying flat against the chest, therefore compromising support and comfort. In a case like this I would go up a band size and allow for a slightly larger underwire and cup to compensate for the room her breasts need to breathe.
Always check your underwire for proper fit, especially after lengthy wear and tear. Under excess stress the underwire can sometimes snap or poke into the side of the breast tissue and neither of these look or feel very nice.
A proper fit should be painless and beautiful. Take care of your girls, girls!
Lace and Love,