Is lorazepam safe to use for an 87 year old female who is also currently taking sertraline hcl?

Risk of fall with Lorazepam is very high at her age. However, there is no interaction between these 2 drugs.

You don't mention doses or reasons why she takes these meds. Taking both ,especially in very elderly people, is risky for symptoms of drowsiness, dizziness and even confusion. Her prescribing physician who knows her best is more qualified to answer this question.