Our very confident fearless 7 year old decided to worry about "how hot" Florida would be. First words off the plane - but its not THAT hot! It was just regular hot. Have no idea what she was expecting - we tried to tell her it would feel like summer at home, blah blah blah. She just didn't believe us.
We know exactly why this happened too...a schoolmate came back from Florida in Feb. Our daughter told the class she was going in May. The teacher AND the classmate exclaimed together "OH IT WILL BE SOOOOO HOT IN MAY!". Well what can you do?
Your neice may have heard some stupid comment about the swimming pools, and she'll probably be fine the minute she gets to the pool. Don't add your stress to hers by stressing over her stress. Sounds like she's already doing a fine job herself. You might never know what she's heard and what image she has conjured up in her mind, so all the well intentionned calming words might never help. Afterall, if she's imagining a snarling sabertoothed tiger, and you're extolling the virtues of purring kitty cats - your words aren't going to have a great impact. She needs experience - which she won't get till she's actually at the pool.