Scared new pup

My husband and I just adopted a 7 year old mix who has spent her entire life chained up outside. As we expected, it's been rough on her (although it's only been a week). We were told that our two other friendly dogs would make this transition easier on her but she is obviously still getting use to them as well. She is very scared of almost everything and spends much of the day hiding in any corner she can find. We have made baby steps with her, but it's a slow process. She is also a flight risk. A few weeks before we adopted her she ran away from her foster home and was on the loose for a good two weeks! Does anyone have any suggestions on how we can make this a smoother transition, or suggestions to keep her from running? (We have a fenced in back yard and she slipped her collar and tried to jump it on night one at our house, my husband caught her mid air!). Again any suggestions on things we can do to help her out would be greatly appreciated! We know this may be a long process but we are hoping to help make it easier on her!

Are there any good dog trainers near you who would do one to one ttaining with you and her? Did you get her through a rescue, they might be able to recommend a trainer.