。
She tends to talk too much.
Literal
She [topic-は] talk-too-much tendency [subject-が] exists.
Two patterns at once. ~すぎる ('do too much / be too X') stacked on しゃべる gives 'talk too much,' and ~傾向がある ('to have a tendency to') frames the behavior as a general pattern rather than a single instance. 傾向 ('tendency, trend') is the formal noun for an inclination — slightly more measured and observational than the casual ~がち ('tend to,' often slipping into negative habits) or the loaded ~癖がある ('have a habit of'). The whole sentence reads like a careful observation about a person's character — the kind of thing you'd find in a personality assessment.