Does your aunt still have capacity to decide for herself? If so, my understanding is that if she says no, you can't overrule it. It's only if she is incapable of making decisions that you can take it on yourself, or if she gives you the authority to act in her best interests, for example if she is physically incapacitated or unable to get to a bank. That's what we were told when we granted POA to our children, anyway.
I'm not a lawyer though, so someone with more professional knowledge might be along to say differently.
How do I help my sister to stop feeling like a victim?
It Must Be Autumn Even Though It's Not September....
