Welcome to the world of fanfiction writing and writing in general! Unless you've already written before, so then I'd just say welcome to FF&W! Okay, now for the actual review.
Well, it's short. There's nothing going on at all, and having more written down might help. Actually, it would help since this doesn't effectively serve as a prologue, to be honest. Prologues are typically short, but they serve a purpose and are relevant to the plot. Whether they illustrate an event that shapes the story or is the catalyst for your story, they're still relevant and people would know how they relate later on. In this prologue, however, there's almost nothing going on at all. Alia is an eevee who lives in a tree. The prologue tells us about how she goes in her bedroom and the prologue ends. I can't help but wonder, what was the point? You really should write more down so readers can get an idea of what they're reading, especially plot-wise.
And I got three more nitpicks I have to mention. One if your writing style. In some cases, it gets wordy and kind of wanders on and on, then repeats itself. Take this sentence for example:
The tree trunk home she was born in was a worn hollow tree.
You say she was born in a tree trunk home, and then repeat that it was a tree, except you mention it was hollow. This sentence could be condensed so that you don't repeat tree again. One possibility would be like this:
She was born in a hollow tree that was her home.
Of course, this isn't a perfect rendition, but I hope you get the idea. Try not to repeat things because that can slow down your story pacing wise. This applies to most of your sentences you've written so far, especially the bit about the peg-stairs inside.
She reached the top, and her bedroom opening welcomed her, as always.
The description here seems to be lacking, since I could assume her bedroom is warm and cozy, but you haven't exactly told us. Mainly, we don't know how it welcomed her. Alia could just be tired and her bedroom welcomed her as a sanctuary of rest. Or she could happen to really like the wallpaper in her room and it was welcoming every time she looked at them. See, you have to describe a few things, otherwise you leave readers in the dark. And readers don't like the in the dark about much at all.
As for the last nitpick: you spelled 'prologue' wrong.
And with that, I wish you well on writing this story. I can't gather much information about it just from this prologue, so I guess I'll have to keep reading to find out.