I really don't see an 800 gram animal making it to 1500 grams by December. That would be one heck of a long shot.
Add in the tendency of females at that size to go off feed for the winter, and I don't think there is much of a chance there.

Too many factors against this idea--the value isn't equal, and unless you have a female that eats like a mammal, you're not too likely to win in the end.
How old is she? That will tell you how fast she's growing, and you can calculate how big she's likely to be in December.