None of your options is really bad (although I would not use the present subjunctive, and probably wouldn’t have occasion to use the present simple in this context either), but none of them strikes me as particularly natural either. If I’ve understood your meaning right, I’d say “She is dreaming of him writing her.”
And yes, in American English, the “to” is optional. It’s not a case of leaving it out — in Old English, the case system made the word “to” unnecessary.