Brisk read.

[Isis]

People do venture into the writing forums occasionally - at least, I hope they do, because I just posted work as well. XD

First off - spacing your writing helps. It looks like you had this indented properly when you typed it up in a word processor, but to post on forums you've gotta put a space between paragraphs. Dialouge can be clumped together for three to seven lines if you have a lot of that, so it doesn't seem too spaced out but is still easy to read.

Next: The dialouge. There was...well, there was a LOT. Dialouge is a tricky thing. I think you have the brother-sister thing down pretty well. However, you don't want to have it just be two disembodied voices talking - make sure that there's some description or action while the talking goes on. You have some, indicating tone of voice, as well as what's going on in the scene. That's good - there just needs to be more of that. Maybe when she's talking to the Willow you can provide more of a description of the tree. Does she imagine a face appearing on the trunk? [I do -- Pocahontas style. That's just my imagination's preference, though. And that's why description is important. Try and show people what you see.]

Your spelling didn't jump out at me as messed up and it didn't register in MS word, but I'm no copy editor. Vennila is better at that. I noticed that you could use more commas in some places. Example:

He knew she would win, but he didn’t want to be the cause of her unhappiness - for this was her element just as swimming was his.

My grammatical additions are in bold.

She loved the way the leaves were shaped, (and<not sure if I should put comma or “and”>)

There are two ways you could do it. You could put an "and", or you could put a semi-colon, [;] instead of that and in the place of the comma.

Overall, I liked the story. Combinations of cute, interesting, eerie...I'd like to see more of Andrea's thoughts and emotions emerge as you keep writing. It would really help bring the story alive - and as we read about her adventures, however crazy they be, we would still relate.
Keep writing. ^.^b