Is it okay to consider publishing in my first year of PhD?
Whatever you do, you will want to cultivate a good working relationship with your supervisor, so I'd advise against doing something she dissuaded you from just because strangers on the internet told you to. Talk it out with her.

That said, not a single PhD student I've known wrote/writes a relevant portion of their thesis in their first year, and the advice I have constantly been getting from faculty is that early in the PhD is the time to think about publishing other things. There will most likely be a time when your thesis takes all your attention, and by then it's certainly too late to worry about publishing elsewhere.