Absolutely. There's a million one ways you could go about this, especially for a ten year old. As people suggested, her being ridiculed/coerced by the community into silence could cause her to let it go. Maybe she'd develop an insecurity. Personally, I'd go with something more physiological, where, say, MC was in a "foggy" state during her time through the portal. Nothing really stuck when she left. Or maybe she comes back and develops a high fever, and when she comes to, she can't even remember. Let's face it, if you're introducing magic into your story, anything is possible. Lastly, you don't ever have to specifically tell your audience how vividly she remembers the place. You can workaround this issue simply by what and how you choose to convey it.
Ever listen to radio programs? The kind sponsored by Red Rider BB Guns in the Christmas Story. THOSE BASTARDS!! THEY SPOOFED IT! Can't wait to watch if for the umpteenth time. OFF WITH ITS HEAD! FA RAH RAH RAH RAHHH...RAH-RAH RAH RAH! But the real ones and none better than War of the Worlds for an example. Bottom line...Believability. A sharp hook with the right bait is just the beginning. Once I was scared beyond shitless, imagined the long-white living room curtains started walking toward me. I was ten. They tapped a fear in the darkness. Sleeping in a new house without furniture, just curtains. Drawn with folds to look like twelve foot tall robes worn by hooded KKK monsters who chanted. No shit. They walked and chanted and glowed. Had I been black, I'd-a died of fucking fright. Tap her fear. Can't have a time portal without a ten-year-old kid scared-shitless. Beyond scared-shitless. I like that...unless of course it's my ass in the sling.
Kind of ironically, the more people keep suggesting similar things, the more I start thinking maybe they're good ideas even if I didn't originally think they'd work in my story, haha. Proof that the more people who say something, the more you believe it! I didn't like the idea of the portal travel itself making her "foggy," but I'm warming up to it for certain reasons. And the last point you make is a good one, but how much she remembers/believes plays a big part in the story. What I've described in this thread is really only the beginning.
I'm going to have to disagree. Kids are often much more trusting, naive, and curious than adults. What she finds in the portal isn't scary at all. Will she be startled and somewhat scared at first? Yes. I think anyone would be, but not in the way you've described. And fear tends to make memories stand out and remain vivid. It might work if the story were going in a different direction, but, for the purposes of the rest of the story, I can't have her scared of it.
