The griffin who is an old friend of Rainbow Dash is Gilda.
Gilda is introduced in the season 1 episode “Griffon the Brush-Off,” which originally aired on November 12, 2010. Rainbow Dash explains that she and Gilda knew each other from Junior Speedster Flight Camp, establishing their friendship before the events of the series.
Gilda’s visit to Ponyville creates tension because she treats Pinkie Pie and several other ponies rudely. Pinkie eventually throws a welcome party filled with pranks, but Rainbow reveals that she—not Pinkie—organized the jokes. Gilda becomes angry and leaves after Rainbow refuses to abandon her friends.
The episode initially presents Gilda as an antagonist, but later stories give her more sympathetic development. In “The Lost Treasure of Griffonstone,” she reconnects with Rainbow Dash and gradually becomes friendlier toward Pinkie Pie. Her species is usually called “griffon” in the show’s English terminology, though “gryphon” is also a common real-world spelling.