Does she become fearful at the sight of the leash or is it just when you try to walk her? I fit is at the sight of the leash then she probably has had bad experiences with them such as abuse and could think a leash means she has done something bad but if it is jst walking I think it would be more fo she is not used to being walked and has probably never been exposed to it or even is not used to waering one. Maybe that's how she got away from her old owners because she was off leash?
Either way you should slowly introduce her to wearing a leash and walking. If she chews on her leash you should teach her that's bad and that she can't chew on that or you can get a chain leash so she can't chew through it.
to get her used to wearing one slowly introduce her to it and put it on her at first for 5 minutes at a time. If she chews on it tell her no. If she is good at waering it reward her and reward her after you put it on so she learns it's good to waer a leash. When she gets better at this you can increase the time she wears it. Always supervise her though when she wears it to stop from chewing on it.
As for walking, you can start on this after she gets used to wearing a leash. Even if you only go on 2 or 5 minute walks at first that is a start. Reward her if she starts walking. Make it a fun and exciting experince by offering treats and a lot of praise and attention. Then she will associate walks with this. Don't give her the chance to ly down so once the leash is on then walk right away. If she trys to stop or ly down just keep going and give a lot of praise and get excited about her walking and continuing to walk. Say good girl, lets go, yay, good walk, ect. in a really excited and happy voice. I think taking a leadership role in this case would also be beneficial so she sees you are in control of the walk and what happens and not her so you decide when to walk and when to ly down and rest. Expect a lot of resistance at first and maybe some fits or tantrums but do not give up and do not pay attention to bad behaviour when trying to walk her. If you give in to any tantrums or just let her ly down and stop she will see that she is in control of the walking when you need to be; if you show confidence and leadership your dog will respect you and follow and be more confident in herself. If she sees you are nervous or worried she will be too.
I agree that it will take time but she will learn eventually with possitive re-enforcement

All dogs like and need to walk and some of them just need a little extra help

Let us know how it goes!
