My Mum can not receive Realm invitations

We have sent a ticket and still not resolved. 
 
Before the update went live, my Mum was in the realm playing without any issues. She was on the server when the update went live. Mum closed it to update it, my Sister then entered the realm on the latest version (She owns the Realm), I joined her shortly after. My Mum then tried to join and couldn't, she clicked on Minecraft Realms and that is when the advert to start a trial or buy a realm came up for her. 

My Sister then left the server to try some troubleshooting and noticed my Mums name was not on the invitation list and everyone else's was. My Sister re-invited my Mum and even closed the server down and tried relaunching it to see if that would send my Mum an invitation.

I think there is a major problem to be honest. We are all running in the latest version and all have it on New Release on Java, PC. My Mum has uninstalled and installed it. Also logged in and out. 
My Sister has done the invitation prosses correctly and she has put in her username correctly. It still says invitation pending on my Mums side.
 
I have attached a file showing what my Sisters end shows and my Mum still receives no invitation on her end after many attempts.
 
I hope there is a way you can help us with this as she STILL can not get invitations after she was playing fine a week ago.