The good news is, if she is like this, she is exactly the sort of dog that is easy to train, she is easily motivated.
You do need to make sure food etc is out of her way, which for a lab probably means not left on the worktops at all, but in the fridge, microwave, cupboards etc. The more times she is able to steal food from the worktops, the more she'll try it, so it'd a viscious circle. If she never finds anything to steal up there, she'll eventually give up trying, but that will be months/years rather than weeks.
Re: the sofa thing, use food to make her bed a great place. Frequently 'lure' her over to her bed with food and when she is on it say 'bed' and give her the food. Feed her meals on/next to her bed, leave bits of kibble in there when she is not looking so she can find them, give her her kong to eat on her bed, keep her toys in her bed when you tidy up, throw some food on there for her if she is on there when you walk past. All of these things will make her think bed = wonderful, place where all the food is, sofa = bit boring really.
As for the stairs, keeping all the bedroom doors closed so if she goes upstairs all there is up there is a boring old landing might work after a while, but otherwise, I'd invest in a stairgate for now.
Supervision is the key to not chewing things, plus making sure she gets plenty fo exercise and things to do (training, games etc). An adult lab ideally needs 2 hours plus of exercise a day, split into 2-3 walks, some of which should ideally be off lead. A tired dog is a welll behaved dog and if you are watching her and she takes something that isn't hers, you can replace it with something she is allowed to chew. Also make sure she has lots of chew toys of her own. If you can't supervise her, put her in the kitchen if she doesn't chew anything in there, even if you're just going upstairs to bath the children. Prevention will eventually mean she doesn't do it anymore.