That's fine.

Ice was a special kekkei genkai used by one person and from there no one else could really replicate it. If Sakura's mastery of water nature is good enough I see no reason why she can't learn to superfreeze her own jutsu. Originally water was meant to be unreliable due to the fact you often need a water source for it to be strong, but the 2nd Hokage could just use moisture in the air to create water at his own convenience. If you'd like Sakura to get to that level she can. At best, for now, maybe the water gun technique is the most reasonable and once she gets better a dragon would be easy?