Hi Rebecka – You may have picked a hard one with Mrs. Streep. As I study photos of her, she doesn’t strike me as having terribly distinct features. Also she’s widely renown as an elegant actress, highest in class, which makes it difficult for me to push her into the less elegant world of caricature.
While I think you’ve done a good job with your sculpt, I don’t immediately recognize her as Meryl Streep. But then I see it a little more compared to this photo:

Here’s my annotations over the photo:

I think your mouth shape is too far of a departure from Streep’s smile shape. I tried to outline that in the annotated image. Note how the right corner of her mouth (screen left) hooks up more than the left corner. The contour where her lips meet has a unique wavy shape while the top lip contour is fairly straight across horizontally and the bottom lip has a consistent U-arch. I recommend focusing on this shape and exaggerating it.
Again given her elegance, I would generally avoid accentuating wrinkles – only accentuate essential wrinkles like her crows feet, possibly under her eyes, and the corners of her laugh lines (which you’ve done pretty good). In the annotations I tried to highlight contour these features to emphasize in blue and the areas to keep smooth in yellow.
Hope this helps, but I really do think she’s a hard one to caricaturize.