Double hmm. I had never heard of el cabello before. From this it sounds like some regions use pelo for all hair, and some use cabello for head hair and pelo for animal/body hair. http://www.spanishdict.com/answers/133732/pelo-vs-cabello
Seems like it's better to err on the side of caution and use cabello for head hair and pelo for other hair.
Pelo can be used in all instances of hair or fur. It ncludes human animal or plant. So any hair.
Ie a peach or a kiwi have hair = pelo. Body hair = pelo Animals = pelo
Sub categories of other types of pelo narrowing the definition: Cabello: is only and specifically hair on a human head, for which you get a haircut. Ie: "Ella va a cortar su cabello". (In México) outside of Mexico it is ok to say. "Ella va a cortar su pelo".
Barba is only and specifically used on the face of "Men". But NOT Women!!
Note: in some regions because pelo is used for animals or body hair. It is insulting to use pelo when you should use cabello. Ie: Mexico. But in other regions it is ok to use it. As often the use another word for animals.