This construction is not used to say "se mettre debout". The adjective "droit" is used to describe posture; it means "upright". However, to say that someone got into an upright posture you wouldn't use the construction "mettre droit(e)". (Similarly, I think you wouldn't say "put yourself upright") Instead, you would use the word "posture" and the verb prendre (prendre une posture droite).

s'est mise droit,s'est mis droit,s'est mise droite

This construction is not used to say "se mettre debout". The adjective "droit" is used to describe posture; it means "upright". However, to say that someone got into an upright posture you wouldn't use the construction "mettre droit(e)". (Similarly, I think you wouldn't say "put yourself upright") Instead, you would use the word "posture" and the verb "prendre" ("prendre une posture droite").

s'est mise droit,s'est mis droit,s'est mise droite