First off, what you are envisioning is potentially very bad. Ownership isn't some sort of club. By making her a joint owner, you are giving away half of the house to her. It can have serious implications to you: it could make it hard to sell the house, it could make you ineligible for medicaid, it could make it impossible for you to get a reverse mortgage. It will have potentially bad tax consequences for her if she eventually wishes to sell it (she will get your low basis, rather than the stepped up basis at the time of your death).
Further, property passing by joint ownership is the same as those passing by will or other laws of succession with respect to MD inheritance tax. Further, MD doesn't tax (currently) property passing to child or other lineal descendant.