I am not a fan of that technique. I am a strong mounter and I can quickly halt a horse if it moves while mounting. If the horse suddenly walks off as my leg is swinging over the just correct the horse with the reins making it stand still. A few times like that and the horse stands perfectly still until I am mounted, settled in the saddle, rein coat domed to the saddle and spread out behind me. I then pat the neck, good boy and with a gentle squeeze of the legs move out.
I don't need lunging.
I also feel the lady was not that good at mounting herself.
Try this sometime.. With no girth, NO girth on the saddle, just a simple western saddle thrown on the horse with pad try mounting???
It can and is easy to do IF you have a strong mounting techinique and keep your weight close to the horse.
Some/most people will pull any saddle regardless of how tight it is cinched up over on the horse.