Tried to change site URL, all posts are now missing

Hi, I really hope one of you can help me. My girlfriend runs a WordPress site – https://rosiejeanreynolds.wordpress.com. Tonight she tried to change the URL of the blog to poetrypromtly.wordpress.com using the ‘Change your current username and discard the current account (you will not be able to change your username back)’ option.

However, when she did this, all of her posts disappeared in both the front and back end of the sites. We’ve tried everything we can think to recover them and have been scouring forums.

Could anyone offer any help? I’m afraid neither of these are very technical!

Thanks in advance.