My opinion: at 6 weeks you will be back to how you looked pre-surgery. I would just keep it to myself. It will also give you a good base-line to your progress once she starts complimenting you when it starts to come in. You are not lying to her, I don't think you have some duty to disclose it. You are doing this for you, not for her.
Now if she asks you about it point blank, then I would casually mention it, or you can say its due to meds. But if you tell her I think it will just add to the stress of waiting for results and she will be looking for them just as hard as you will be.
Are you doing fut or fue? Fue you will be healed up by then but FUT she may feel/see your scar during the first months.