Collaborating on a file using the iphone app.

Collaborating on a file using the iphone app.

I'm new to Zoho documents, coming in from google documents. A friend and I do a lot of collaborating, some of which is on her phone. So, I have shared the file, and given her read/write permissions on the document. And the collaboration button is on.
She was able to access the file on her laptop, but now when she tries to access on the phone application for IOS, it is telling her she can read only. 
My understanding is you should be able to access the documents anywhere/anytime. Her IOS is up to date, and we have tried everything to get this to share.
Out of ideas, but...the permissions look right on my end.