chewing up everything in sight?

I'm sure some others with more experience with this type of thing will be along.  But, an immediate fix while you are working on training would be to crate her if she can't be supervised.   She's still really young and will probably grow out of a lot of this too.  Also, some friends of mine have a husky/golden mix that does this and they've cleared the counters of pretty much everything they could.

This girl is to young to be left unsupervised. Either crate her when she can't be watched or tie her to you with the leash. Shes just being a puppy.

20 months?  Thats almost two years... I think its still a puppy but I do think she should be growing out of this by now.  Maybe she has separation anxiety.  I would agree that if you cant leave her safely then you should look into crate training her for while you cant be there.
 
Edit:  I know I may be wrong about 20 mos thats what it looks liek to me if wrong please correct.

remember that you have only had her 3 months. Who knows what her prior owners did or didn't do with her. I agree - contain your dog if you are unable to have your eyes on her.
 
Also, congratulations. You have a dog who isn't grown up in the head quite yet- it can take about 6 months to a year longer for them to mature mentally (espcially labs, setters, eetc).
 
You officially have a dog who enjoys the game of "Counter Surfing". Solution? Block of the kitchen or totaly kid proff it till your furkid "gets it" that this a major NoNo.
 
Invest in some Fooey or Bitter Apple for things he may show an interest in (like another expensive basket - ouch, your wife must have been ANGRY). Invest in some interesting and entertaining toys. Filled and frozen Kongs will most likely help keep him entertained and out of trouble, as will a good chew toy like a bone or nylabone (flavored and flavor last forever).
 
Good Luck and hopefully his sweet heart and good looks will win over your wife.[]

Crate or watch.
 
A twenty month old Boxer should already have set her teeth into her jaw, so this sounds like chewing that is more related to her trying to calm herself, or she could simply be a dog that has had no consistent training (often a reason they get dumped at a young age - not a cute pup anymore and the humans can't deal with the same behavior in a 70 pound dog).  Try to take her to classes right away so you can establish communication with her on a consistent and understandable basis. 
I have found that it is easier to use clicker training with a large adolescent dog.  No yanking involved. []
[linkhttp://www.clickertraining.com]www.clickertraining.com[/link] has a trainer search.

I agree with the others, crate train your dog.  Your dog is in a area of your house in which she is able to reach for things.  If your unable to watch her, put her in an area that don't have anything for her to chew up.

Crates are a wonderful invention...........