I submitted my PhD thesis 6 months ago and I have yet to receive news regarding viva exam. Is it appropriate to contact graduate school to inquire regarding this matter? My supervisor is on leave for 3 months and I cant contact her

I would chase it up at this stage. I thought most universities had an agreement (3 months or so?) about the period between submission and viva.

It was supposed to be 3 months. I sent my thesis on August last year and I checked with my supervisor last November to make sure everything was fine. To my surprise, person in charge from graduate school did not send my thesis to examiners until last November. Thus they have wasted my time for almost 3 months.

I think it's perfectly reasonable to ask someone to find out what's happening at this stage, especially with your supervisor being off, as they would normally be the go-to person for you to ask.

Yes.
It took my university 4 weeks to post my thesis and only did so when I chased them.
I graduated in absentia and they didnt send my certificate until I pestered them for 4 weeks by email.
They lost my address and then apparently lost the bloody certificate and had to reorder it.
I was about to make the trip into the university itself to have it resolved face to face on Monday but received a text from DHL on Friday to say it will be delivered to my home on Monday.

In my experience large companies are absolutely stuffed with employees who are a complete waste of space. Universities are included in that. Never be afraid to chase them or escalate things if they start hiding behind emails.

Hey,

I have experienced similar issues in the past where I needed to chase up someone for some feedback. I ended up waiting just over six months to receive something that should have taken one. My advice? Do all that you can to chase this up. During my own personal issues, I sent numerous emails to find out what was causing the delay, and often received unhelpful replies and excuses as to why there was a delay. Ultimately, this was only sorted due to me chasing up the issue, and sending emails of complaint to higher members.

This is important to you so I wouldn't just wait for them to get back to you, put the power back in your own hands and chase them up until you receive what you need.

A.W