Myra is 51 inches tall.
We'll use Susan as our base for this. She is 50 inches tall, and ignoring Myra or now, we move on to Elanie, who is said to be 2 inches shorter than Susan - therefore, Elanie is 48 inches tall. Now that we know this, we can return to Myra's information which says she is 3 inches taller than Elanie, which would mean she is in fact 51 inches tall.