MyCloudEX2Ultra Access from a different network

I have a MyCloudEX2Ultra set up on my wifi network at home. I can also access it via the app on my iPhone. Occasionally (I think after app upgrades) I need to reconnect to the drive via the app. But it only seems to be possible to do this from the home network and not from a cellular network or alternative wifi network. If using a different network the “Available Devices” are not available under my cloud so cannot be selected to be added.
Can the device bew set up to allow this. My daughter is in the USA on a different wifi network and can no longer connect to the MyCloudEX2Ultra.
Help please !!