She wants it online by sunday.
Ok then so it is now Wednesday afternoon (GMT) and you want someone to teach you how to set up a webserver, secure it from attackers, hackers and spammers by Sunday.
And how much were you thinking of paying for getting five or more years experience in three days??
She wants it to be hosted on her own computer.
Does your sister have a fractional T1 line with a fixed IP to her "own computer"???
Because ADSL is fine for a testing and development server but NOT for production servers, been there, tried it, gave it up as a bad idea. Also, many ISPs block inbound port 80 (HTTP) on their 'domestic' services to prevent people doing just what you are proposing.