This is lovely. The white roses almost make her look paler. I'm not sure if you meant to have her as the opposite of what you were painting behind her... she's primarily dark (hair, dress), with only a small amount of her lit. I'm curious what she's thinking... she's in a lovely garden, but her face is stony. Is someone coming upon her when she'd prefer to be alone? (Rhetorical, please don't feel obligated to answer.)
The difference in her hair from black to shining silver is somewhat abrupt in my opinion... which I hope you'll take with a grain (or handful) of salt as I'm not much of an artist. I only noticed it because her hair seems larger than her head. Not that it can't be exactly the way it is (mine often is), but I probably would have stopped after the intermediate gray section, without continuing on to the silvered area. That appears more proportional to me.
Is her dress black or very dark green? Considering this makes her seem almost funereal, all in black, and even the roses don't have color.
I notice that her hand is holding her skirts, but it doesn't seem to affect the lower lines of the skirt... you can't see a gap at the bottom where her shoes peek out, for example. If it doesn't affect the hemline, you might want to make it affect the drape of the skirt less. A handful of fabric on any dress I wear is probably going to raise the hem, even if only a bit. (Not that I make a point of wearing fancy evening gowns all that often...) Perhaps a bit of lacy petticoat, just something different than the sleek fabric you used for the dress.
I apologize if I have commented on things that may seem negative, I tend to run out of words for "lovely" when I find pictures beautiful. You said you did this without a reference... I think that's quite impressive. You might consider looking at references for the points I've mentioned, just to get ideas of how to address (or ignore) the things I have noticed. "Without reference" doesn't have to mean you don't bring to mind things you've seen before, though I understand wanting to do it yourself, and make a point of not thinking about anything but your painting.
I love the roses. The light through/around the bushes is wonderfully done. I think the garden would make me feel peaceful if not for the stony woman in black giving me the evil eye... well, not that much. She's just looking this way and it somewhat detracts from the "peace and quiet" feeling.