。
She likes the pattern on the plate.
Literal
She [topic-は] that plate [genitive-の] pattern [subject-が] is-pleased.
気に入る (lit. 'enter the heart/mind') is the standard idiom for taking a liking to something — the が marks the thing liked, with the implied subject being the person doing the liking. The progressive ~ている here marks resultant state: she's been in the state of liking it (and continues to). 模様 ('pattern, design') refers specifically to a decorative pattern — the kind of thing you'd find on tableware, fabric, wallpaper. The Japanese tradition of decorated tableware (染付, 九谷焼, 有田焼) gives this kind of comment a familiar context for connoisseurs.