Thank you for the opportunity to help you with your question!
AEL is an acute angle, its angle is less than 90 degrees. Your not going to AEL by using ER because its not dividing the acute angle, AEL Angle can e bisected by drawing an equal angles dividing AEL. If AR divides AEL then it would be possible to use ER.
THANK YOU FOR THE OPPORTUNITY
Please let me know if you need any clarification. I'm always happy to answer your questions.