Can't Upload to /Uploads/2015/10 directory

We have a brand new install of Ubuntu server 14.0.4 LAMP and a fresh install of WordPress 4.3.1. We hired someone to migrate our Drupal site to the new WordPress site. All was working good except our Web Developer could not use FTP or FTPS(ssl) to install updates so I installed SSH2 and she was able to use that for her updates to plugins in WordPress. Again, all was well until yesterday she could not upload any files to the directory.

/home/username/web/wordpress/wp-content/uploads/2015/10

Starting at the /web folder through to the /10 folder she is listed as the Group and Owner of those directories with 755 permissions. The strange thing is all the files in the /10 directory now are listed as Group – www-data and Owner – www-data with a 664 permission and she cannot upload anything to that folder. This is the error:

“The uploaded file could not be moved to wp-content/uploads/2015/10.”

What I don’t get is she is the group and owner of the /10 directoy 755 and she still can’t upload to it?

I think the obvious fix would be to make her the group and owner of all those files again but does www-data access as well?

So, what would have caused this to happen and how do I go about changing the group and owner on all those files in that directory?

Thanks,