Perhaps she had a dream and that's what she's trying to say. I would just encourage her to be artistic and maybe refocus her attention on different things to draw. Don't make a big deal out of it.
I suspect it's just an active imagination (and that's a good thing!). Most kids her age are afraid of monsters. How often do little ones make you check under their bed, in their closet, etc. to make sure there are no monsters? Using drawings as an outlet for her normal fears seems like a healthy thing to me. However, when in doubt, always run it by her Dr. She sounds like a smart kid.
Hi bheron. It's not necessarily meaning anything is wrong with her. Do the monsters have any facial features, tattoos or something that could be related to someone that you know? It could be that someone is touching her, making her feel uncomfortable, or she's just been watching something she shouldn't have. I would sit down and have a talk with her make her feel comfortable and make her tell you how she feels, but don't worry if she doesn't want to it's very common children don't want to talk to their parents about their life. Also make sure that you spend time with her. If you have any questions feel free to ask.
Sincerely,
AdultHelper
Is there any TV or computer images where she has seen the monsters,does she have siblings that would show her pictures friends maybe at their houses on play dates , there are many scary things on TV now including Vampires and Draculas it seems to be a vogue ..I doubt there is anything wrong with her, children do like to draw strange things , but it may be worth asking her has she seen them any anywhere .