Icloud backup failed iPhoto cloud library

II've got a problem. My iPhone 5 backs up to iCloud just fine, but my wife's iPhone 5s just stopped saying it doesn't have enough space anymore. No drastic changes or anything. Under iCloud, storage, manage storage on my phone shows just my iPhone and iPad backups. On hers it shows those two but above it it shows iCloud Photo Library with an additional 6.8 GB of storage space eaten up. A few thoughts I have here. One, iCloud Photo Library on her phone is not enabled. I did update our MacBook a while back and it uses the same iCloud as her phone. Could that have turned it on and be doing this lack of backup space? She's even tried deleting multiple unneeded photos. She's already bought the 20 GB plan over a year ago for the added storage space needed. Can I turn off the iCloud Photo Library in the iCloud manage storage and not lose the photos/videos that are locally stored on the phone/iPad? Sorry if it's a stupid question, but I just don't want to irrevocably lose anything.