If the two of you have talked about her becoming your slavegirl, why not go all the way?
Remember that slaves have never had any rights. The two of you need to discuss whether rights are something she wants to surrender.
Also remember: it’s critical that the two of you have a deeply established and cultivated trust before any such discussion can begin.
But maybe she doesn’t want rights. Maybe freedoms mean nothing to her.
Maybe all she wants to be is your little slavegirl.
Try it for a weekend. Then try it for a week. Then a month. And if all goes well, try signing a 7 year contract – at the end of which, she’s offered freedom once again.
Consensual slavery is a big decision. Don’t rush into it. Make sure you both have plenty of trial runs and plenty of information.
And if it works for you and you’re both happy, don’t ever apologize.