Good find Jimbo
I have a couple of other tidbits on Gisela that may help find more on her.
She played the French and Wimbledon in 1928 as Fraulein Enger, so her marriage was sometime on or after July 1928. Also, Wimbledon sources lists her as PG Enger. Thus her first name started with a "P" and she went by her middle name of Gisela.