Reset the phone as new, then set it up again to her iCloud account.
Then unless she, or someone with access to her phone, who also knows the passcode to get to the home screen and install a jailbreak app (which you would see alongside your other apps), then it is not jailbroken.
There are numerous ones available now. Many of which only work under a specific version of iOS:
Cydia
EvasiOn
TaiG
Pangu
p0sixspwn
Redsn0w
Absinthe
PwnageTool
Sn0wBreeze
GreenPois0n
LimeRa1n
Regardless, since you've reset the phone as new, you won't find any of these. And if it had been jailbroken before you received the iPhone, it no longer is.
Which still leaves the mystery of why apps would appear and disappear, but I don't have a suggestion for that.
We have done that a couple different times. she has had it for a couple months now and it's been fine up until the last couple days. She has been able to get system updates and everything has ran fine until now.
How do I know if phone was jail broken?
