I think she is quite lovely. She looked good in Normal People (although probably not quite as thin as in the novel where her character definitely lives the SG lifestyle) and she has lost a lot of weight since the start of her career.
Oh, I thought she was totally gorgeous in Normal People! She's decently skinny all over and quite delicately-featured, but her top half is definitely her strength, and those collarbones and xylo in particular. I was a big fan of the high-school Marianne scenes, where they dressed her in these slightly baggier clothes which made her look like a little bird. Apologies for the influx of gifs...
I also really like the scenes in Italy and this one in particular; when the light hits her you can see all the bones in her xylo.
There are quite a few nude scenes too where you can really get a good look at her whole body, and she's certainly no Kardashian. I for one was really pleased to see a character on a TV show with a body type long-touted as adolescent and non-sexy; it was nice to have a bit of representation for the A/B-cup girlies!