There are a lot of ways to play slide guitar. Wendy plays an acoustic guitar tuned to open E.
The strings from lowest to highest are then E A E G# B E. This way she easily plays in any key.
With her left hand, she frets the strings with a socket wrench (14mm) used as the slide. Having learned to play in Mississippi, she wears the slide on her fifth "pinkie" finger.
This frees her to make a minor third or flat seventh behind the slide.
She plays individual strings, and chords with her right hand.
In most situations she uses an electronic pickup and runs it through an amplifier for a rich sound.