I get the impression this pony is thinking 'get this owner away from me' too.
Let's read between the lines here.
'I can't handle her... I cannot get hurt by her anymore.'
This horse has reacted with sufficient violence to injure her rider/handler. Great selling point to start out with! But why might that be....
'We don't have proper equipment... i know she hates the saddle and is ok bareback'
Why would you ever try to work with a horse without proper equipment? I define that as a safe, flat area to work in, a decent bridle, a bit that fits correctly and is not rusty or worn, and a saddle at least vaguely fitted to that animal by someone with a bare idea of what they are looking for.
So she hates the saddle- had a saddle fitter out at all? Ride a horse for long in a saddle that doesn't fit right and you're looking at a sore, fed up, potentially violent animal. Imagine walking for miles in badly fitting shoes. No wonder they play up. Maybe the saddle is a good approximation for your horses- this is a little round pony.
'I have had her since she was 3'
This mare is now ten years old and the seller has had her for seven years. I get the impression she's been trying to work with her on and off (mostly off, her back that is) with minimal success, several bruises and possibly fractures.... It also means though that much of her ridden career has been with this owner. In what sounds like an ill fitting saddle. No wonder she's fed up!
That's not to mention whether her teeth have been examined, her feet given a good once over, and a vet been out to check for other sources of physical pain. Pain can come from the strangest places to cause violent responses under saddle, which is why I mention feet- a horse I knew started rearing when his owner tried to ride him despite showing no initial signs of lameness- a good examination and x ray revealed degenerative changes in the bones of the foot and I think the ultimate diagnosis was navicular.
'can't have the trouble with her anymore...'
Now that statement just screams show up with a trailer and forget the $100, you can have her...! Although...
'will learn to be trailered this weekend..'
This smacks of a misplaced confidence! If this pony has given her this much trouble just for riding I wouldn't guarantee she'll have trailering down in two days- especially given the lack of 'proper equipment'... trailer or large cart I wonder...
Good luck Goldie, I hope that despite the fact your owner 'can't have the trouble' with you, she takes enough care that you don't end up taking the nearest wrong turn to an auction with an unscrupulous buyer...