Hi Florencia, You could try using a smaller clipper which makes less noise, and let your horse stand next to other horses when they are getting clipped to get used to the sound. If you clip the horse for the first time just do short sessions, for example first day the body, second day the legs, third day the head and touch ups. it may take a day or two and in those days it will look stupid to have a semi clipped horse, but that way the horse gets used to it a little more, doesn't throw a fit due to being tired or annoyed. Also always have someone help you hold your horse, so it doesn't hang itself in the cross ties or is able to kick you, and the person could hold the twitch for you. If your horse is getting dangerous, I would use sedation for your own and your horses' protection.
I would start with not Starting the clipper and just make her feel it on her body without the Sound. Then turn on the Sound on without clipping her. Just make her used to the Sound. You Can always put Earpuffs in (things that reduce the Sound).
my trainer gave my pony a drug to make her just a little sleepy so she wouldn’t kick or bolt off again (we tried the first time with no drug, did NOT go well, ended up cutting herself with a crosstie after she bolted) and it helped a lot and we got her clipped. my trainer said that it should put good memories of the clipping to the horse and they will remember that it wasn’t so bad and that they didn’t resist it last time.