Legal Question in Real Estate Law in Maryland

There is no such thing in MD. If you own it, you own it. She may have some sort of rights to reimbursement from you if she paid and you AGREED to give her a share of the property (even orally), but she would need a written agreement to get any sort of ownership interest.

The closest concept is "adverse possession" which can give someone ownership rights by default after 20 years of continuous occupancy. However, other elements need to be established and your facts (occupying for 8 years with your permission) do not suggest anything close to a valid adverse possession claim by the other tenant.