Re: TNG: The Body Electric by David Mack Review Thread (Spoilers!)
^^ Data 2.0 had Akharin restore Lal's positronic matrix because he knew that doing what Soong had done for him -- taking a new matrix and putting the stored memories into it -- wouldn't actually bring Lal herself back, just make a new copy of her. In the same way that Data 2.0 is not actually the same individual we followed throughout TNG, but is actually a new copy of the original.
Data 2.0 wanted to revive Lal, not create Lal 2.0.
We don't know that for sure because the subject of building a new brain to house Lal's memories isn't brought up, that I can recall.
"If I hadn't tried, the cost would have been my soul." - Admiral James T. Kirk, Star Trek III: The Search for Spock