Yes, it could. She'll have to be careful to maintain a neutral lockout.
My mom's elbows hyperextend something like 20 degrees, and given that elbow lockout is necessary during liftoff and bringing the bar over your head for safety, I was wondering if there was any extra caution necessary when benching for people who can hyperextend their elbows significantly. Could the weight stress the hyperextended joint too much?
Yes, it could. She'll have to be careful to maintain a neutral lockout.