Hi Barbara.

Dear Jessica,

Yes, this absolutely could be developmental.
As she's reached a new level of cognition, she's more aware of the world around her and she's putting 2 + 2 together in new, more sophisticated ways. It's why, for instance, a child who was never afraid of a neighborhood dog suddenly is frightened. A new level of reasoning has kicked in that goes something like this: "Whoa! This dog is a lot bigger than me. It could hurt me if it wanted to." Logic and experience -- that it's never hurt her before -- aren't relevant at the moment.
You are likely not going to know what has set her off and, frankly, it could be almost anything. My best guess would be either something she overheard from age-mates, or it could be related to entering first grade, or kindergarten, whichever is relevant for her. (Readers: this letter was written before the Boston Marathon, so it's not the result of the bombings although Belmont is next to Watertown and was also in lock-down. LW, have her nightmares exacerbated since that event?)
Also, it may very well be fear of monsters et al -- it's typical for the age -- but she may not share that because she thinks she's too grown up for that. So give her permission to be afraid of monsters as well as the remedy: "You know, I read that some kids your age are afraid of monsters, so just it case, let's use the Monster Spray." I'm assuming you already have a night light in her room....?
Have you talked to her during the day about her night wakings?
Having a conversation in the middle of the night is never a good idea; it tends to make matters worse. But it can be helpful to talk about it during the day -- it is not going to plant the idea of having a nightmare -- because it can help her develop coping skills. Ask her if she remembers what made her afraid? Ask what she thinks you could do to help her when she wakes up? It's OK to say, "I can't come into your room several times a night," but avoid saying, "You're too old for this." The idea is to enlist her in the problem-solving. In fact, you could ask her playmates if they ever wake up during the night and what helps them? (You might want to pre-screen that by asking the parents first!)
My favorite solution with a child this age and older is to create a spot for her on the floor in your room and it might work for you since she's already coming into your room. Offer it up as a question so she will feel some ownership: "What about ....?" and have her help create the spot -- a pillow, a few blankets -- so it's not cozy, just sufficient. Tell her she can come sleep there in the middle of the night if she feels safer. Some kids can do this without even waking the parent, although in the beginning, she might just gently tap you to tell you she's there. Some parents think this creates as big a problem as what it solves, so yes, it can mean she will come to your room on many nights. But you are more likely to get back to sleep, and, while this trek into your room can go on for a while, it tends to be sporadic after the initial spurt, and kids tend to outgrow it quickly.
Keep in mind that her fears are likely real; her requests, maybe not; they're just a way to keep you with her. So the other solution is for you to go to sleep in her room and then, gradually, wean yourself away. I think that takes more stamina by the parents, though.
Some kids go through a stage where they just need to know you're checking on her. The "bangle solution" of my former colleague is worth a try with your daughter; it might give her the reassurance she needs to go back to sleeping through the night.