。
She's a middle-aged fatty.
Literal
She [topic-は] middle-aged fat is.
中年デブ is blunt and unflattering — 中年 ('middle-aged') combined with デブ (a colloquial, somewhat rude word for 'fat person'). デブ is written in katakana, which is common for slang and informal words. This sentence is crude and would be considered rude in most contexts.