This app was mentioned in 30 comments, with an average of 3.97 upvotes
Some people might not know anything about the app, and the source just cites the beta opting procedures. The article included some info about it, and it's where I got it from anyway, so might as well credit them.
I thought about linking its Play Store entry, but you have to be a beta tester to view it. Linking an article might just save them some hassle.
What devices do you have? TeamViewer should work though. Anyways try,
I personally find Inkwire better than Teamviewer, as there's less places for my grandparents to go wrong.
https://play.google.com/store/apps/details?id=com.koushikdutta.inkwire
It lets you see their screen, draw on it, and talk to the other user for free.
Try this. I have not used this app myself so can't tell if it works but it claims it could show you a remote device's screen. From this you could atleast tell her what to do.
Now, this may sound silly, but have you considered a low tech solution? Something as simple as creating a basic case jerry rig with a mount and a tilted mirror might make sense over having two different phones that you need to set up / charge / manage.
As for Apps, apparently you can do this between two android devices using an application called Inkwire but I have not used it before so I cant speak for it.
I just had another interesting idea. Google hangouts. There are programs to record and save what is happening on your android screen, so theoretically, you can call the google hangouts on your iphone from the android, fullscreen your camera on the android, and record the screen on that while using your iPhones hangouts session as a viewfinder. This sounds like a major pain in the arse though, and in this case I would just opt for a DIY low-tech solution.
The Moto X is new for $289.99 and the Moto G is even cheaper. Both offer reasonable stock android performance that should be plenty for a non-techie.
Look into apps like Inkwire or TeamViewer that let you provide remote assistance.
You should try Inkwire it even has audio!
If both your internet connections are good, check out Inkwire https://play.google.com/store/apps/details?id=com.koushikdutta.inkwire
Try Inkwire. I personally haven't used it though.
https://play.google.com/store/apps/details?id=com.koushikdutta.inkwire
Would not work with airplane mode though :p
Inkwire is pretty decent. https://play.google.com/store/apps/details?id=com.koushikdutta.inkwire
Have never personally used it, but I think you may like Inkwire.
Not possible over USB, but there are many apps which can do this over WiFi, such as InkWire
Try Inkwire. It doesn't do remote control, but it can do screen sharing.
https://play.google.com/store/apps/details?id=com.koushikdutta.inkwire