Generally head size does lead to a bigger snake, even when you look at sub-saharan ball pythons. Their heads are massive and some of the snakes are found 3000g+.

I have an 07 male who just turned about a year old and is almost 1000g's empty. My spider female is around 800 and she was born july 07. Then some are smaller like my male pastel who is only 400g and he is about as old as my spider.

I would say, to answer your question, she probably will be bigger and it is very possible you have a slow grower.