mod_rewrite to hide subdirectory

[atlex2]

Hello,

I need to hide an embedded directory in a URL site2.com/site2files/ <-- need to remove that and just see site2.com for the files in /site2files/

Here's a visual representation of my file system.

site1.com
Document root:
-file
-file.html
-folder/
-site2folder/ (Important!)
-file
-functions/ ::need to be accessed by site2

site2.com --if it wasnt auto re-routed to /site2folder/
Document root:
-file
-file.html
-folder/
-site2folder/
-file
-functions/ ::need to be accessed by site2

site2.com/site2folder/
site2folder:
-file.html
-folder/
-file

site1.com and site2.com both point to the same server.
I can't use virtual servers or mod_rewrite document root because I need the documents in site1.com accessible by site2.com
I have requests for site2.com rerouting to site2folder/ using php header("Location: and $_SERVER
I don't want my users to see site2.com/site2folder/ I want them to see site2.com/ and still access the files in /site2folder/. I was thinking mod_rewrite but I'm terrible at that..
Again I want to pretend like the directory doesn't exist and just use the top-level domain.

Thanks!
BTW
--I found this online and it DOESN'T work
Am I doing something wrong?

RewriteCond %{HTTP_HOST} ^(w{1,3}\.)?site2\.com$
RewriteCond $1 !^site2folder/
RewriteRule (.*) /site2folder/$1 [L]