Is it permissible to marry one's maternal aunt's daughter despite the aunt's ex-husband's rejection, due to the suitor being a relative of his ex-wife, knowing that there is affection between the suitor and the fiancée?

The guardian does not have the right to prevent his ward from marrying a suitable match for flimsy reasons, due to the potential for discord and corruption therein. The Prophet encouraged marrying a suitable match. If the guardian refuses, he should be advised and persuaded; otherwise, the girl has the right to refer the matter to the judge to marry her.