Do I have to accept the invitation to be a bridesmaid?
Technically, you don't, but in reality it's pretty hard to
say no. If it's a financial issue, be up front about it and
see what the bride-to-be says. If she really wants you in
the wedding party, maybe she can help come up with a solution
or will ask you to participate in another way, such as being
a guest book attendant or a reader at the ceremony.