A Bright Tomorrow by Janet Lambert (1965)
But when tragedy struck the Jordon family, Bitsy suddenly realized she needed other people, and that friends couldn't be turned on and off like water faucets. As the roommate of two young career girls, Bitsy discovered that sharing problems, as well as joys, was illuminating and often very helpful.
Janet Lambert, the popular author of more than forty books for teen-age girls, has written a moving yet ebullient story. The delights and the sorrows of being a member of a big family and the frustrations and rewards of pursuing a career in one of the world's most exhilarating cities are sensitively portrayed and Bitsy herself emerges as a sympathetic and charming heroine. (from the inside flap)