All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
You are not obliged to order your servant to stop reading the Bible if she is reading it to herself. This is because Islam does not prevent the People of the Book from practicing their rituals and does not, at the same time, oblige them to follow the rulings of its Sharee‘ah. Nonetheless, if this woman is calling others to believe in what she is reading, then you have to get her out of your house. In fact, we advise the Muslim to only allow honest and religious Muslims to live among his family.
Allaah Knows best.