My dog is a Great Dane mix and is supposed to weigh 90 pounds or more. She weighed about 97 pounds until we moved. After we moved, She lost about 17 pounds. We don't know if it is because she's gotten more exercise or if she hasn't been eating. Could anyone tell me a reason her sudden weight loss?

It could be anything. Weight loss is generally an indicator to get your dog checked out... something as severe as liver damage or diabetes, something as minor as worms or stress. Or just more exercise. You know how she's been acting best... so take her into a vet, explain, and blood/fecal tests would probably be a good idea, just as a precaution. If she hasn't been eating, you DEFINATELY want to get her in... immediately. That's like one of the top 3 signs you're supposed to watch for as a general sign of illness.
... or it could be stress. *shrug*

he might be on a diet

Depends on the new environment and if she is on a regular feeding schedule. When you feed your dog once or twice a day...you can actually tell if they are eating less, which can clue you to medical issues. A dog will usually eat less when there is a major change in the routine of things. Watch how she is eating. If she has a sharp decrease in her food intake and a lot of weight loss, consult your vet. About a week will tell how she is adjusting to her new environment.

No, no one can tell you why.
Vet. As soon as possible.

it could be a change in the enviornment as cause of lack of eating, or my there could be a tapeworm

You would know this better than we would over the internet. Is she eating? How can you not know if she's eating? Does she have a large, fenced in yard to run in now? You have not provided enough information for anyone to know what's going on.

You really need to see a vet. This could be a symptom of diabetes, cancer, or just worms.

worms maybe? see a vet, thats not good!

you should check your dog for worms.

she could be stressed from the move but a lot of times a thyroid disorder or diabetes can cause a drastic weight loss. time to go to the vet.

worm, too hot , i n the summer most dogs lose weight , my dane does, he weights 156 lbs lol he need to lose some
worm him ,weight him and re check after one week /ten days or so

Sudden weight loss is usually a sign of worms.

Get her to the vet and check her for worms. Worms will cause a great deal of weight loss in a dog.