She literally said herself "i can't win dawg", do y'all even read
She asked for Momo to call for Luffy only after Momo did prohibit her from fighting. Plot saved Greenbull ass. Why would plot not let Yamato fight if Greenbull can beat her???
Because he can't, she would win and plot makes Momo not wanting to be helped and saved again by someone else that he believed wouldn't stay in wano.