How best to approach non-paying condo association member?

We live in a duplex condo so there is no real association. We do have a condo agreement (somewhere). We've lived here for 11 years, have yet to get a copy of the bank statement. An owner took $500 out without consulting us to hire an attorney to tell us to take our christmas lights of the deck by Jan 31. Now we find out she hasn't been paying her condo fees, got rid of the lawnmower and told us to by our own. We're not really sure where we stand or what we can do about these ongoing problems. Any advice?