How to edit on iOS8 a shared Numbers spreadsheet

Hi,

On my Yosemite account, I created a Numbers spreadsheet that I am saving and sharing on iCloud.

I can open it, see it and modify it on my iPhone (iOS 8).

Now, if I share and send the link of the sheet to my wife, she can open it and modify it using Chrome.

Here is my problem, I cannot find a way to open it and modify it using her Numbers app on her iPhone. The only option she has using the link I sent her is to save a copy of my shared spreadsheet.

Any help would be greatly appreciated!

Thanks a lot!!!

Julien

PS: Sorry if this was asked before!