Email address being used by someone else as their apple ID?

I wanted to set up an apple ID for my wife. I tried to use her gmail email address, but it is already being used by someone else as their apple ID. It was linked to a different email address that is not her.

Why would someone use her specific email address as their apple ID?

Could they somehow use it in a way that would hurt her? It wouldn't be linked to our finances, but it still makes me uncomfortable.

Is there a way to stop them from using it?

Thanks!