My dad remarried after my mother died. He just died, and she is still occupying the house.

My sympathies to you on your Father's death. First of all, you need to see if your Mother had a Will and if your Father had a Will.  If Wills exist, they need to be probated and your rights to the house are included in those documents.  If not, your rights are decided by the laws of intestacy.  Normally in Texas, a surviving spouse would have a life estate in the homestead no matter who owned the house after your Father's death but without more information, I can not tell you for certain as she may have signed away her rights to the life estate in a Premarital Agreement. Please consult with a lawyer in your area regarding your rights as you may have several options available to you.