AJ,
From everything you've said, you didn't do anything wrong. For whatever reason, which you may not ever know, you + her just weren't a match for each other at this point in your lives. That happens sometimes.
Unless, you treated her poorly (and you've given no indication of doing that here) then a card like the one you described is innocuous; provided you don't have an agenda attached to it, i.e. you hoping she receives it and contacts you.
As I see it, you're still confused and need to uncover
your reasons for sending it and
your reasons for not sending it.
I just don't want to send a card and have it negatively impact her holidays.
This statement is the crux of the problem . . . it's you thinking you that you can possibly know what her reaction might be.
Why set yourself up for more disappointment? She knows where you are. Let her reach out if she wants to.
This ^ is the type of thinking you need to consider. The reason behind sending the card or not needs to be connected to a purpose that
holds meaning for you. For instance:
Send it
simply because you wish her well.
Send it because (if this applies) you know
you'll later wonder in the future "what if I had only . . ."
Don't send it because you've already received indication (by not returning a measure of reciprocal care and interest in you) that she's not interested, and since she's not interested, then deep down
you know you don't want to continue pursuing her and thinking about her.
Don't send it because you know (deep down) that you'd be sending it out of hope that when she receives it she'll contact you, and if she doesn't contact you
you'll feel disappointed.
Know
your reasons for sending it or not.
Don't base your decision on any type of fantasy of how she might receive it. That's something you cannot know or control.