if she resided with you for more than 1/2 the year, assuming the child meets the relationship, age (under 19 or under 24 if full-time student), the support rule is that the child did not provide over 1/2 their support, not whether any other person provided over 1/2 their support you would be the person eligible to claim the child.
do nothing to change her return. eventually, the IRS will send both you and your aunt a letter asking for them to amend their return to remove the dependent. you should do nothing. if your aunt does nothing, then the IRS will send a second letter asking for proof. The notice should specify what the iRS wants as proof. this would likely include documents to show the child lived with you for more than 182 nights.
