Her lavish dress stood out at the party.
The hotel lobby was decorated with luxurious ornaments.
She was wearing gaudy, extravagant jewelry.
派手 is the general word for flashy or showy, whereas 華奢 (かしゃ) specifically implies extravagant luxury rather than just bright colors or style.
贅沢 focuses on excessive spending or indulgence, while 華奢 (かしゃ) focuses on the visually ostentatious result of such luxury.
Written identically, 華奢 read きゃしゃ means slender or delicate (of a body or build), while 華奢 read かしゃ means lavish or showy.
The word 華奢 is a combination of 華 (flower, splendor) and 奢 (luxury, extravagance). The exact historical derivation is uncertain, but the kanji suggest a meaning of 'flowery luxury' or 'ostentatious splendor'.