My mom's dog has been eating hair . . . why has she been doing that?

My mom's Maltese has been eating both her hair and our Chocolate Lab's hair. She's possibly also been eating my cat's hair. I'm guessing she probably eats it off of the floor. Both yesterday and today she puked up large hairballs. I'm wondering if anyone knows why she does this and if she needs to go to the vet. Thanks!