Wow - that is a fairly complicated song for someone picking up an electric guitar for the first time! I admire your penchant for a challenge! But I think you might want to start with some easier songs to play and work your way up to that one.
It is likely that the guitarist in the video is muting the unplayed strings by lightly touching them with one of her fingers. In the second video you can see her reaching over the top of the fretboard with her thumb to mute the bass strings so she can strum all six strings with a steady up and down strumming pattern but only play the top four or five or middle four strings.
In some cases she may be muting certain strings with one of the other fretting fingers by angling her finger to allow it to lightly touch and thus mute the strings that are not to be played. In some cases it may be a non fretting finger or the edge of her hand that might be muting certain strings (such as the first skinniest string most often tuned to high e).
With practice you will learn to strum and intentionally miss the 6th string or the 6th and 5th string. It comes with a great deal of practice. But if you can learn to mute the strings that are not to be played, you will eliminate the chance you might accidentally hit a string that is not supposed to be played. If you can't comfortably reach around with your thumb, you can use the tip of your index (pointer) finger to mute the bass string.
It's not shown in your linked video, but another technique for playing two non adjacent strings simultaneously is to pluck them at the same time using your thumb and middle or index finger. You can also do this with a pick and your middle finger. This is sometimes referred to as a "pinch".
Don't be discouraged if you can't do any of the foregoing right away. It takes a great deal of intentional practice to master these string muting techniques. While you are practicing those, try learning some songs with some basic chords that don't require so much string missing and muting.
Good luck and have fun on your journey towards becoming a great guitarist.