This entirely depends on how far back the iOS is.
Three versions back, yes, then you will have problems due to that alone.
Current version and just the latest stuff to update? Probably won't have problems if you don't upgrade, but if you do, you could be an involuntary beta-tester for Apple.
Here is what I would do:
- Make absolutely sure your wife knows how to reboot. Not just turn the screen off, RE BOOT it.
- Make sure she knows how to actually close apps. Not just, "hide them" but close. (Hint: double click the button, swipe up on all the tiles that appear until no more appear.)
Do that first, chances are, it's fucked up because it hasn't been restarted.
But find out the latest version of the OS, and the version installed on it too.
For the WORK stuff, ask the IT department at work about it. If they won't support it, then she shouldn't be using that device for work. Make THEM do the thinking on that stuff.
The interfaces don't change THAT much so she should be fine.
I always wait a few months before updating the OS to let other people deal with the bullshit bugs that get introduced and fixed.