It is better to know ones metamour in my experience. The fear and talk inside your head lessons when you at least meet and get to know them. Its hugely beneficial that metamours are civil and respectful to each other at the bare minimum. I think you are wise to ask to meet them. Its not a yes no decision$ you aren't her dad. You are working on thia together. She doesn't need to ask permission, she needs to consider you and communicate how she plans to work this out. Then you do the same, that is how it works. This is negotiating... That has nothing to do with permission. I don't think its fair she even ask.
Anyone want to be friends on Facebook?
Send me your name via PM