Recover Vista administrator user account

I was the administrator on a Vista system. I thought I made my sister a administraor so after verifying that she has administrator previliege, I deleted myself's user profile. The laptop however, remained her as a standard user. Everytime she needed changing, computer asked for my password, can't make any change because it won't accept my past password because me as an administrator profile is completely gone. Can't do safe mode, system restore also because they all need administrator' password. help

thx

kmli34291