If you can put up a dog gate to keep them in the room where the back door has access and put in a dog door. Then make sure the room has a hard surface which is easly to clean. Spray the bitter lemon on everything you dont want them to chew and then get them chew toys.
This is the closest to what I'd recommend, too. I don't know how high your fence is in the back, or how much room you have, so you'll have to consider that in giving her unrestricted access to the back. Labs are roamers by nature, as well as being chewers while they're young. You don't want her clearing your fence, or going through it, either! Was she microchipped where you got her? Both my guys are chipped, and the chip number is also on a tag on the collar along with a number. Our number is on a different tag and the vet's number is on the rabies tag.
My guys now stay inside during the day, in a 9 x 12 room with ceramic tile floor, plus the kitchen and carpeted hallway. There's a widespace barrier closing off the living room. They have their beds, loads of toys, water (food is given twice per day; if they freefed they'd be tanks!), indoor pads if they need to relieve themselves, and NPR for company. They use the pads and whoever gets home first just disposes of them. (I tried that doggy litter; forget it! Barley thought it was to eat and it isn't all that neat or even absorbent anyway. Plus it's expensive).
We don't have a doggy door and I still don't expect to put one in. After the trouble with Rory's poor stomach after he ate all those acorns, plus the coyotes right outside the fence, we're taking no chances. As soon as we get home we run around outside with them, play fetch and catch and run. They also love frisbee.
I haven't seen bitter lemon, but our local pet store (ok we're in the boonies, don't forget) carries bitter apple. Any bitter stuff should work, but you have to apply it every day. Our guys used to use the outside door mats as banners to carry around the yard; I learned the benefits of spraying daily to discourage seeing those as toys.
Crate training is fine, especially at night if you don't want the dog sleeping with you (look who's talking, though!). But you'll be away for, what, 10 hours each day? You don't want to leave a dog in a crate for that long at a stretch.
I'm so excited for you! Labs are such great dogs and there's so much to love about them. If this is your first pet, especially as an adult, you may find from time to time that you question whether or not you're up to this, but hang in there, it's worth it!
