Sorry for bumping up an old post, but I was looking for "base runs" in her earlier lessons. I went through them all one by one, but couldn't find them. However after I thought about it for a second I realized what it was.

First you need to understand this...

(C Major Scale for Beginners: Lesson 1)

http://www.guitartricks.com/lesson.php?input=10664&c_id=2&ch_id=10&s_id=363

When you are playing the alternating bass notes on the C chord you are alternating between the 5th and 6th fret with your ring finger. On your 4th measure of C you are about to switch to F.
Do this:
-Hit your first bass strum on the 5th string
-Strum strings 1-4
-Pick the 4th string open
-Pick the 4th string 2rd fret (middle finger)
-Pick the 4th string 3rd fret (ring finger)
-Leave your ring finger where it is and make an F chord
-Strum strings 1-3

You'll continue on to do another measure of the F chord with your alternating bass. Then you will reverse the process back to the C chord. Sounds confusing, but if you take the time to learn the Major C scale that i linked above you will not have a problem connecting the rest of the dots.