。
Mother is always interfering in my personal life.
Literal
Mother [topic-は] always my personal life [in-に] interfere-only is-doing.
~てばかりいる is 'is always just doing X,' with ばかり restricting the activity to that one thing and a negative-judgment overtone. The pattern is common with complaints about repetitive behavior. 干渉する ('interfere') takes に for the thing interfered with, and 私的な is a な-adjective meaning 'private, personal.'