But for getting a horse used to it, you could do the same as for golf carts or carriages or other things - have her follow it around first, so she's "chasing" it in her own mind. Then pass it, then it passes her, then do circles around it, etc. until she finds it less interesting?
the quick release knot dont work thankfully i wasn't wearing my seatbelt.
just about 150kgs of power chair land on my skull missed by less than 2 inch(5cm)
You're trying to lead her from it by tying her to the chair?
That seems like kind of a Bad Plan. If you can't hold the lead yourself while leading her, I'd at least probably fix the lead in such a way that basically if she pulls at all, it'll just release. (Because a loose horse is better than a loose horse with a heavy power chair attached to her head.)
Also, I suspect you really need someone able-bodied to help you get her used to things.
I'd probably start by having someone else in control of her and letting her sniff you and the power chair all over, then run the chair a bit so she can hear the noises it makes, but keep close enough that she can see and smell it's still you and not OMG SCARY NOISY THING.
Then progress to someone leading her walking next to you.
Then someone leading her from your chair (if possible) so that if something does go wrong and they get dumped or something, they can, well, run away. Or stand up to control her.
THEN when she's okay with all of that, lead her from the chair yourself. But not actually tied to the chair.