Yes, Moondragon Did At One Point Join The Avengers But Only For A Short Time!Before Joining She Had Assisted The Avengers In There First Battle Against Thanos. She Latter Aided Them Again Against Thanos Along With Help From Captain Mar-Vell And Drax.

During Her Time On The Avengers TeamThey Fought Thanos Again, But The Most Noted Battle In The Time She Was An Avenger Was The Fight Against Korvac. During The Fight She Used Her Powers To See Into Korvac's Mind, In Doing So She Saw Korvac's Plan To Save The Universe By Ruling It, She Believed This To Be Noble; She Then Stayed Out Of The Battle Until KorvacDejected, And Committed Suicide.