I have muscle. I look lean and muscular when I'm lean, but not so much if I'm not. If your body fat is higher (and I don't mean high, even low normal) it's not as obvious though. I mean, I'd expect more definition in her legs, but you can see she has muscle in her deltoids.
Also, different body types respond differently and her training hasn't been for muscle for quite some time I would think.
Feel obliged to add that most women are *much* healthier at her body fat level than with a 6 pack. She's in good shape, but probably not so lean that she's interfering with her menstrual cycle. A lot of the "fit" types are setting themselves up for osteoporosis.
ETA: if you look at bodybuilders in their off-season, most won't look the same as on stage. Many not even close. Some gain a ton of fat, but that's not recommended. I have very little time for Siobh, but she's actually looks like she's in a lean enough to be sustainable without being so lean that you're starving situation. Even though she seems to have a terrible lifestyle and drinks far too much.