Wow, if she's that size at 18 months she's gonna be a monster when she's done growing! I've got one girl just like that, she's not even a year old and she's already almost 800g. I get the feeling she's gonna be a big one .

But yeah you should definitely give her some more time before you try breeding her. With a snake like that that's growing that quickly I'd say wait til she's 1750-2000g. Shouldn't take long!
Good luck