I cannot select a previous backup on time machine

I'm trying to upgrade my girlfriends mac to the latest OS X but she asked me to pull out some files for her and save them on a flash drive for her first. The files aren't on the Mac now but should be in previous backups.

Her mac has been connected to my time capsule from the very first day she got it so all her files should be saved on my time capsule.

When I entered time machine to find those files, I was only able to go back a few months "her Mac has been backing up for about a year and a half now"

I can see the purple stripes on the right in time machine that go back way before the oldest point that I can access, but the lines are kind of shaded and I can't click them! So it seems like the data is saved and the time capsule is recognizing the Mac but for some reason I just can't select the earlier dates!

So to sum it up

I'm trying to access older backups but when I enter time machine the backups I want are shaded and I cannot select those dates

So far all I tried was to reset the Mac and I did a "hard restart" on the time capsule by disconnecting then reconnecting the power.

Has anyone had a similar issue? What can I do to access those shaded backups?