As with many grandmother-y names, this choice may be coming back into style. It rose 237 spots between 2012 and 2014.
Myra was invented in the seventeenth century by a poet called Fulke Greville as a short form of Miranda--or perhaps an anagram of Mary-- and it quickly caught on with other poets and romantic novelists, particularly popular with the Scots. There were leading characters named Myra in Sinclair Lewis's novel Babbitt and in Theodore Dreiser's An American Tragedy. Later it was the name of the central character in Gore Vidal's 1968 Myra Breckinridge, and plays a minor role in the Divergent. trilogy.
Myra was as high as Number 158 in the 1880s; it now ranks at Number 638. A notable namesake is the great pianist, Dame Myra Hess.