[Mononokay]

If you have a backup of her phone from around that time you might be able to get the .ipa off of it, assuming it's on an older version of iOS.

[Wowfunhappy]

But it's likely 32 bit only and won't work anyway on anything newer than iOS 10.

Actually, there's a decent chance it won't even work in iOS 10 or would have major glitches, because legacy compatibility in iOS just isn't great in general.

And it's literally impossible to downgrade to an older OS version after Apple has closed the signing window.