Is it considered haraam not to inform the neighbor—who used to ask for everything shamelessly—about the availability of an empty apartment in the new residence for parking her car?

You are not obliged to inform your relative about the empty apartment in your new residence, and there is no harm in your unwillingness to have her as a neighbor due to the harm she causes, for "there shall be no harm nor reciprocal harm," and it is permissible to get rid of a harmful neighbor.