why dont you try repeativly puttin the rolller over back and taking it off agen
dnt do the girth up at first just gradually tightn and loosen til she happy to have it on the back tightened and taken off agen without freaking out. as she is 5 she will need longer than a 3yr old to learn.
i am in a posistion where i can offer the care and homes for a few of these neglected horses. does anyone know who i can contact to offer special homes to these horses?