All 3 of the photos are really cute. You did a great job capturing her expressions.
I also like that she's dressed in pink and you've got her in front of a pink floral background.
I think you used too much vignetting in these pictures. You're right noticing how dark the backgrounds in these pictures are. Since these are spring-time photos, I would hope to see brighter colors & brighter backgrounds.
Vignetting is not necessarily bad. It's a good technique to use to focus the viewers' eyes on your subject. But I think too much vignetting detracts from the photos. Try to dial-down the vignetting.
It looks like you took these pictures in a nice shaded area. Because of this, the pictures are slightly cool in color temperature (very slightly blue). Under "white balance", try increasing the temperature a little bit to warm up the photos. Again, this will also match the brighter "spring-time" theme of these photos.
You mentioned that the girl's lips were very red. I wasn't sure where you wanted to go with that...did you want to tone down the redness of the lips or did you want to bring out the redness? In the 3 photos, if you wanted, you actually have room to "bring out" the redness of her lips a little bit. In Lightroom, select the "Adjustment Brush" and increase the saturation slider. Then brush over the girl's lips to get them a little redder.
Or, if you wanted to bring down the redness (perhaps in her cheeks?), you can use the "Adjustment Brush" and decrease the saturation slider. Then brush over her cheeks to decrease the redness.
SrisonS is correct that you can also use the "Luminance" sliders and decrease the red slider. This would act globally throughout the entire photo, so any areas of red (not just the girl's lips & cheeks) would be affected by this. You can also try the "Saturation" slider and decrease the red slider, too. See which one works better, if at all.
In the 2nd photo, you can try brightening the girl's eyes. Again, use the "Adjustment Brush" and increase the Exposure slider, then paint over her eyes. If you wanted to also bring out a little more color in her eyes, you can also increase the "Saturation" slider (also within the "Adjustment Brush" window) at the same time.
Anyway, I'm just nit-picking at some possible options for post-processing. I'm certainly no expert at portraits or anything, so please keep this in mind.
So please feel free to ignore any or all the above ideas.
However, if you do try any of the above, please don't overdo any of the above adjustments. Be subtle with your post-processing. You don't want people thinking that the photos are unnatural or "Photoshopped".
Overall, though, I think you did a great job capturing these photos. I also liked that you preserved the details in her dress, and nothing was "blown out" or overexposed. I also like the "catchlights" in her eyes, too.