Hi Amber. Reflowing doesn't really do much when it's water damage. You cleaned the board which is the right thing to do. Sometimes that is sufficient. The danger is if the corrosion is occurring underneath the various IC's on the board.
However, if nothing works, you need to start troubleshooting the board. Check the main power rails for shorts and if you find one, you have to figure out which component is dragging everything down. This is not an easy task if you don't have the schematics and boardviews.
As for the data, they reside in the NAND but you can't just take it out and read it, especially if the device was encrypted. If you want to recover the data, you need to get the phone nominally working so that you can transfer the data to iTunes.
If you don't have the necessary tools, I would recommend that you find a qualified shop that can do water damage repair and data recovery.