Mrs. Higgins is a humble lady.

Answer: Option C

Humble : having or showing a modest or low estimate of one's importance.
Whimsical : playfully quaint or fanciful, especially in an appealing and amusing way.
Youthful : young or seeming young.
Vain : having or showing an excessively high opinion of one's appearance, abilities, or worth.
Unassuming : not pretentious or arrogant; modest.

Antonym of Humble is Vain