How long after getting her period will my daughter's breasts grow for?

It varies...: Breast development (or thelarche) is generally considered separate from menstruation (or menarche). And breast size is partly due to hormone levels during puberty, but also partly due to a girl's weight throughout her life. Girls typically continue to grow (in height and weight) for a couple of years after their first period, so breasts tend to do the same over the same period.