Never let anyone take of advantage of you in a business situation. It will only lead to trouble -- more trouble than you will get by confronting the other party.
I know its easy for me to just say "confront her!". But it is really, really important you you dont get sold short. A favor for a friend is one thing, but you are describing a Web Project that is potentially worth thousands of dollars!
We often feel the need to allow this sort of thing to avoid potential conflict. Your friend probably has no idea how you feel; infact, she probably has not even realised the unfairness of the situation.
Just tell her that there are alot of costs involved in E-Commerce Web Development and you simply cant fork out cash for such a project, which is a true statement in itself. She will understand.
P.S This should probably be in the Business Matters forum. Rhs, Jick?