When will my baby stop being frightened and crying when she hears loud noises?

See below. As a child grows up they will become more and more tolerant of loud noises. Your child is showing a normal startle reflex at this point. Some children will always be startled by unexpected loud noises, though they will react in a different way as they grow up.
Depends. This is a hard question, even adults are frightened by sudden, unexpected loud noises. Crying is your baby's way of showing surprise to these noises. These can be scary for the baby. If you anticipate a loud noise talk to your baby in comforting tones, this may help with the surprise.