iCloud photo backups not matching

[convert2mac]

Here is the situation. I am trying to help my sister (remotely). She is getting the constant message that her phone is not being backed up because there is not enough space. Ok..so we go into the Manage Storage in the iCloud in the settings. It shows the next backup size is 5.7 gb. It also shows that the Photo Library will be 5.1 gb of it. So we go into her photos and copy most of the photos and videos off of the phone and onto her computer. We delete all the photos and videos we copied from the phone.
Now when I check the General, Usage, Manage Storage, I can see that "Photos and Camera" takes up 1.2 gb. When I go back into the iCloud manage storage, it still shows the next backup needs 5.7 gb total, and photos are still 5.1 gb.

So my main question is "What photos are selected to be backed up?" because it is obvious that if there are only 1.2 gb of photos on the phone, and it wants to put 5.1...there is something I am missing and not understanding exactly how Apple set up the way it backs this stuff up. It may have been 3 months since her last backup. Is it still trying to backup the photo stream from the past 3 months? even though we have deleted them from the phone? Does that make sense?

Any insight into this matter would be greatly appreciated. And how to get it to just look at the current set of info on the phone.

Thanks, Jerry