PJ is right. Like all great writing for the theatre, there are many ways to interpret this moment (and really, most moments in GYPSY).
Since I'll never play Louise (except in my apartment), I try think about this as if I were directing the musical.
I ask myself, what is Louise trying to accomplish with this line. And, for me, it would be to hurt her mother. Now, being snide and dismissive can absolutely work. But for me, personally, I think it's more hurtful to make the line somewhat sincere, to let Rose know the true damage she caused and that, now, Louise sees her for what she truly is.
"I'm so looking forward to a time when all the Reagan Democrats are dead."