Her elegant bearing makes it obvious she comes from a refined family.
Tips
history
Recorded in 《世说新语·贤媛》 (A New Account of the Tales of the World): 顾家妇清心玉映，自是闺房之秀 - a refined young woman of the inner chambers. Here 大家 means "great house / aristocratic family" (NOT "everyone"), 闺 = inner women's quarters, 秀 = the finest among them.
mistakes
Don't read 大家 here as the everyday word for "everybody" - in this idiom it specifically means a great noble household. Compare 大家 (everyone, daily speech) vs 大家 (great house / great master, literary).
