The reins would run through a D ring from the pommel of the saddle to the stirrup iron to allow her to use the reins in this manner.
From the kentucky.com
Things took a horrific turn when her riding boot lodged in the stirrup iron and Paula was left dangling from the terrified animal as it fled.
From the gazetteherald.co.uk
These included cast iron, the ploughshare, the stirrup, gunpowder, printing, the magnetic compass, and clockwork escapements, most of which were thought at the time to be western inventions.