Good idea, but it could be phrased a lot more amicably. Maybe, "Hi, I'm really happy you like [song name]. Just writing to let you know that you're entirely welcome to use the song in this video, free of charge, as long as you add an annotation crediting me (Zoe Keating) and linking back to my Bandcamp page (URL). Here's an article describing how to do that: [link]. Thanks!"
"FOOL! You dare to use my music on your worthless trinket of a video? Demonstrate your complete submission to my will by adding credits and a link, as directed [link], and I may spare your pitiful life. KNEEL BEFORE ZOË!"
Depending on the musician / band that actually might be the proper tone for the message. Probably not for this artist, but I can think of a few that the fan would get a kick out of that response.
