Advice for a horse that really curls up

[Redcow-hat]

Hi, hoping to get a little advice on a horse I've taken on part loan while my main horse is out of action. She's a very sweet and willing girl but has clearly been see-sawed in the mouth and ridden into a huge overbend by previous owners. The current owner is a total novice and only pootles about in walk.
At the moment we are focusing on manners (standing when asked is an issue) and general relaxation but moving forwards I'd like to break the (very established) habit of coming right behind the contract. She sticks her chin on her chest at all times, including on the lunge and the long reins. I cannot seem to get her to take the contact forwards at all.
My own have only ever been either just backed or very green so I'm unsure on how to break such an ingrained habit in a 14 year old horse! Any advice?

 

[Equi]

Scratch her withers and give her the longest rein you can. Slowly pick up the reins and as soon as she overbends, drop the reins and gently squeeze forward. Repeat.

No idea if this is correct, but its what i would do (and have done)

 

[scats]

What bit is she in? Sometimes in these cases when you have to try and break a habit, I find changing something such as the bit/mouthpiece can be useful, even if just for a short time.
Millie had a dreadful habit of curling behind the contact, except she does it simply as an evasion as she finds it far easier to sit there than take the contact and go forwards.
I’ve found she’s much happier to reach for the contact in a bomber happy tongue, anything jointed tends to cause her to curl up even more.

 

[twiggy2]

Has she been checked by a dentist and I also would look at bits to see if I could find something that she is happier in.