I don't know how she got so good at sucking cock but she is really good at sucking cock.  She sucked my cock years ago and wanted me to cum in her mouth.  I didn't the first time but let her have it later.  It was wonderful and she took every drop and loved it.  She is a true cumslut and I love her for it.  When I am receiving a world class blow job I don't ask where she learned it.   I enjoy it and so does she.