Estate inquiry

The fact that you paid for the property actually doesn't really have any bearing on ownership. If you paid for a property that was partially owned by another person, you made gifts to that person each time you made a payment that benefitted them. You don't provide one critical fact: How did you and your mother hold title to the property? If the deed clearly states that you held it as joint tenants or with rights of survivorship, then you are likely correct, and you are likely now the sole owner of the property. However, if you and your mother were both listed on the deed as owners, but the deed did not specifically and clearly create a joint tenancy with rights of survivorship between the two of you, then, assuming it is a Georgia property, your mother's interest became part of her probate estate at her death and passed either under her Will (if she had one) or under the Georgia intestacy rules if she didn't have a Will. In either case, your sister may actually own an interest in the house, because she may have received a share of your mother's interest. You should ideally sit down with an attorney and figure out what exactly happened. The attorney will need to look at the deed (which is not the Security deed, but is generally a Warranty Deed, Limited Warranty Deed, or Quit Claim Deed) for the property to see how it was titled. Depending on what that says, you may then need to have the attorney help you figure out what happened when your mother passed away. Best wishes to you.

Look at the deed records.  If your mother died without a Will, and her husband predeceased her, her children equally inherit her share, but not yours. You may want to negotiate a Family Settlement Agreement reflecting the amount you have paid but getting your sister to agree, or evicting her, could be difficult.