。
Her face was beaming with delight.
Literal
She [topic-は] joy-color-full-face was.
喜色満面 is a 四字熟語 — a four-character compound — meaning 'a face full of joy, beaming with delight.' The structure breaks down as 喜 ('joy') + 色 ('color, hue') + 満 ('full') + 面 ('face'): the joy-color spreads to fill the face. Yojijukugo are stock vocabulary in formal writing, school essays, and ceremonial speech. Some are essentially literary (一期一会 'a once-in-a-lifetime encounter'), others everyday (起承転結 'beginning, development, twist, conclusion'). The compact four-character format gives them rhetorical weight, often beyond what a longer phrase would carry.