。
Tachibana being all embarrassed is really cute.
Literal
Embarrassed Tachibana [topic-は] very cute [copula-だ].
恥ずかしがってる is the casual contracted form of 恥ずかしがっている — using ~がる to describe visible embarrassment. キュート is the English loan 'cute.' とっても is the emphatic form of とても ('very'). だ is the plain copula. A brief, admiring observation about a character — very natural anime/manga fan speech.