I tour a lot with my wife on the back. Method we’ve always used is:
I sit on the bike holding the bike upright. My wife gets on from the left, puts left foot on pillion peg, one hand on my shoulder other on topbox and steps up onto the peg so she’s stood upright on peg. Then lilts right leg over the saddle onto other side of bike, lowers herself onto saddle.
My wife isn’t short but does have a weak knee so if possible I pull up near a kerb to make it easier for her to step up onto the pillion peg.
It does take some practice but it’s the best method we’ve found.
A friend of mine puts his bike on the side stand, his wife then gets onto the bike ( from the left obviously) in the rider position and then shifts Back onto the pillion seat,he then gets onto the bike.
Hope this helps.