。
The compliment put her in a great mood.
Literal
She [topic-は] this compliment [at-に] completely mood [object-を] made-good.
Two stock pieces. お世辞 ('flattery, compliment') uses the honorific お prefix that has fused into the word — 世辞 alone is hardly used. すっかり ('completely, fully') is a 擬態語 (state mimetic) for total completeness — it's pervasive in Japanese as a way to mark something happening in full. 気をよくする ('to be pleased, be in a good mood') is the transitive collocation — literally 'to make one's spirit/mood good.' The に on お世辞 marks the trigger — what caused the change in mood. お世辞 carries a slight implication that the compliment may have been more flattery than honest praise, lending the sentence a hint of irony.