Hi I bought some items from moumou, and I think it happens because miscommunication problem.
Do you still want the mask now? I think you have 2 options..

1. Want the mask
Get the parcel from post office, and pay her full amount

2. Dont want the mask
Get the parcel from post office, and send it back to her. If want, then pay her a bit postage fee.

I believe in you. No body is right or wrong. Anyway, it had happened no point blaming the responsibility right? Maybe you have to rugi a bit but if like that can solve problem i think is worth it. Hope you can settle this immediately and properly, if not I think it might ruin your reputation in here.

All the best to you.