Hi Navami,
All of the following idioms are fine:
not only... but also... (e.g. "She's not only kind, but also intelligent.")
not just... but also... (e.g. "She's not just kind, but also intelligent.")
not simply... but also...
not merely... but also...
Furthermore, the word "also" is optional in all of these: it would be perfectly logical to say "She's not only kind, but intelligent."
However, your
2. not... but also
won't work -- not because it's not idiomatic, but rather because it's not logical. If I'm going to use the word "also," I need to be introducing a second thing after I've already said one thing is true. But if we were just to say "she's not kind, but also intelligent," we haven't listed a first trait for our "she" to warrant the "also" popping up later, since if she's NOT kind, the only trait we HAVE given her is "intelligent." In contrast, in the examples above that do work, the "not" is negating the "only" or the "merely" or the "simply" or the "just" -- it's not negating the adjective "kind." So in those, "kind" is trait #1, and as such, we can use "also" to introduce trait #2.
Make sense?
Ashley Newman-Owens
GMAT Instructor
Veritas Prep