Not sure if cat is pregnant

This is my nanas cat Misty, she likes to roam and has been gaining weight and her appetite has increased, when stroked she tends to purr a lot  but mostly likes to be by herself. As this is my nan's first female cat she isn't sure as to whether she is pregnant, her nipples have gone a little bit bigger but still we are not 100% I thought we'd check this site for any ideas before arranging transport and time off work to get her to a vet. Any help would be greatly appreciated!

The nipples usually turn pink and get a little bigger on day 21.  A cats pregnancy averages 65 days.  I have a hard time judging from the photos since my cats are slightly chubby.

There are some articles at the top of the forum that will help you out.  I'll get you started w/this one  http://www.thecatsite.com/a/how-to-tell-if-my-cat-is-pregnant

Feel free to ask questions.  Other people will also add information as the day goes on.