While she undoubtedly played an important roll, it is the
song "Saturday Night Fish Fry" that is regarded as the birth
song of Rock and Roll. Mainly the 1949 recording done by
Louis Jordan and His Tympany Five.
[link to en.wikipedia.org]
There are links at the bottom of that Wiki to the lyrics
and an mp3 of the song.

Of course, Elvis played the most important part by making
it "ok" to listen to black music, as long as a white person
performed it.

To this day many of the pioneers of Rock and Roll, mainly
blues musicians from the 30s, 40s, and 50s who's lyrics
saw their way into Led Zeppelin and ZZ Top songs have almost
never received the credit they are due.