Can I sue my condo ociation for failure to enforce covenants equally?

Can a condo owner sue an ociation for enforcing rules unequally among homeowners? One rule we have is that owners may not park in guest parking. If they have guests that are over more than 7 days, they must park in the guest lot. One owner, who has a medical condition (so the board feels sorry for her) is allowed to have her mother park in the guest lot, 7 days/wk, even though she has a spot in the underground parking lot. The ociation has threatened to tow other owners/guests who violate the rule, but will not tow this one individual. Can we sue to enforce the convenent and have her towed? Or, can we violate other provisions of the covenent and sue if they enforce those sections on us, because they are only choosing to enforce certain covenents? IE...they aren't enforcing the parking covenents, so we will put up a birdfeeder (which goes against the covenents). I know we cannot withhold our monthly essment, but what are our legal options?