The way I usually make her go is a moderate speed to me, something I can sit okay and enough to post to. After 40 minutes in good weather around 80 degrees she only has a little sweat around her stifle and shoulder, and under the tack, unnoticeable difference in breath and heart rate, so I think that means I'm not letting enough work go into the trot? For reference about her fitness, her cantering limit is 10 continuous minutes on both leads at working pace, I don't have an issue getting into working canter, just not sure about the speed and impulsion for trot is now that it seems the trot work I've been giving her is too slow/easy. I don't have safe hills or areas to let her gallop, we can only sprint once in a while. My exercising focus is to increase her cardiovascular capabilities.
This is a cruddy picture from months ago when her hock wasn't fused yet, this is her at a slow pace, but it gives an idea about her stride length: