。
Since having a baby, she hasn't gone out much.
Literal
She [topic-は] baby [subject-が] born [after-てから] [contrast-は] much go-out stopped.
赤ん坊ができる literally means 'a baby comes into existence' — a common, somewhat indirect way to say 'have a baby.' ~てからは marks the temporal starting point ('since having the baby'), with は adding a contrastive nuance: 'from that point on (as opposed to before).' ~なくなった (from ~なくなる, 'to cease doing') describes the change of state: she came to not go out. The combination of ~てから and ~なくなる creates a before-and-after narrative.