It would really hurt to find out after a long time being in the relationship. Not that I have a problem with that, but human is wired to own our thoughts, it's like our safe place and treasure house. And if we want anyone inside it, it has to be a willing permission from us,not forcefully.

A lady having a power to read mind might even be worse if she is not very intelligent emotionally, almost all your thoughts affects her mood and they are not necessarily bad ones.