here are pics:

First I must say PRETTY KITCHEN!!!!
As for hood?
A bigger hood would be better to capture fumes, smoke and
grease. HOwever there are many kitchens with a hood that is
the same size as the range. And yes sticks out like yours.
Yours seems fine to me.

I wish I could tell you which is better. For me bigger is
better but I think there are a handful of factors.
1) Space can you go bigger?
2) venting system (powerful is good)
3) how you cook
4) Deep hoods or hoods that stick out can cause head bumps.
Will this bother you?

Hoping the Kitchen Gurus will chime in on what has worked
for them. I can only say in my current kitchen I am
hoodless which means I would take your hood rather than
my ugly mircowave. Yes and I would bump my head a few times
to keep the grease at bay.
smiles.
~boxer

A few more garden web links talking about this very topic.
I hope this helps you.

Range Hood Height - How High is Yours?
http://ths.gardenweb.com/forums/load/kitchbath/msg072057161916.html

Does your vent hood stick out 2 ft? Pics pls!
http://ths.gardenweb.com/forums/load/kitchbath/msg0412440118632.html

Does your vent hood ever bump your head?
http://ths.gardenweb.com/forums/load/appl/msg111952297451.html

Here is a link that might be useful: Past GW link to this argument. Bigger or same size?

Gosh, the more I see copper hoods paired with rich wood cabinets the more I'm falling in love! Your kitchen looks great.

Hmmmm... It looks like the hood doesn't cover all your burners so i hate to tell you this, it won't be effective clearing the smoke.

I think your hood is gorgeous, but I must admit it is not in proportion to the range.
My hood is a custom designed wood hood and I was told to overhang the range by 3" on each side. My range is 48" wide and my hode is 54" wide.
I think if you had done your mural under the hood a little smaller, it would have given the illusion that the hood was larger, but since you kept all of the dimensions the same, the eye cannot be tricked.
From what I can tell, you are really far in your remodel and fixing things at this point would be very expensive.
And just to make you feel better, I think just about everyone of us on this forum has something that really bugs us in our kitchen remodel and it is just a matter of living with it and accepting that the new kitchen is much better than the old.
Overall, I think your kitchen is lovely!

Your hood should indeed have been larger than the range. However, at this point, you would need different cabs on either side to accommodate the overhang. A barrel hood might look visually larger, but with a custom piece it's probably too late for that, too.

In my opinion, the depth of the hood is much more important than the width. Many of us have hoods that are the same width as our cooktop particularly with flanking cabinets. Generally it's a good idea to have a hood that covers the front burners so 24" or 27" are usually recommended. I didn't know this when I purchased my hood so mine is actually only 19" deep. It's powerful enough to capture most things but I do get a little grease on the outside front of the hood that needs to be cleaned off occasionally. If you can get a deeper hood without too much hassle, that would be good but I wouldn't bother replacing your cabinets to get a wider hood.

BoxerPup's Item #4 - we have a 24" deep hood mounted 30" above our cooking surface (per the hood's specs) + we're a tall family (5'10" shortest/6'6" tallest). We never bump our heads on the hood while cooking (or prepping)!

My 6'5" DH did bump his head once...but from the inside of the hood. He stuck his head up into the hood to check it out and when he pulled his head out, he didn't drop it low enough and hit the back of his head on the inside of the front of the hood.

While it probably is too late to change the width of your hood, I would consider Weissman's recommendation to at least look into a deeper hood.

I have to second what Weissman said. I am so sorry - you must be very disappointed and especially since you put yourself into the hands of a professional who really should have known better.

I talked to Trevor at Eurostoves about this (if you are new to GW he is our expert at cooking / ventilation issues).

He explained to me like this - with a 36" range your choices go from best to worst:

1. 42" wide x 27" deep
2. 36" wide x 27" deep
3. 42" wide x 24" deep
4. 36" wide x 24" deep

Your situation is made worse by the fact that your rangetop is bumped out... again, sorry for your troubles. I hope your designer will do the right thing by you and eat her mistake. With your bumpout you should have a hood at a minimum 27" deep.