Question regarding upgrading the OS on an iPhone 4 and the iCloud activation lock

I was given an old iPhone 4 from a friend of mine. The phone is currently on IOS 6 and is working fine. Apparently the phone was either never used, or the former owner, my friends mother, reset it before she got a new one. There is nothing on it, but here is my concern. Under iCloud settings, there was an email address there that belonged to my friends mom, which was her Apple ID. I will not be able to contact her to get the password because she had a stroke a while back and is not in good health. From what I understand, if the phone is upgraded to IOS 7 or above, it will prompt for the Apple ID and password of the former user, if they had the phone setup using iCloud and "Find my iPhone." I spoke to my friend and she has no idea if her mom used the feature or had it enabled. I was able to change the Apple ID to my own, and that is what is in the phone's configuration now. iCloud is currently off on the phone. I am just trying to get this phone setup for my wife, who currently has a 4, but because it is only 8GB, cannot upgrade to IOS 8, and she would like it to be. It would hold her over until she could get a new phone this summer. Am I going to turn this phone into a paperweight if I upgrade it to IOS 8?? Any help would be appreciated!