Sweat isn't always a sign of exertion tbf. I used to be bodybuilding lean and it was only the first year when I had weight to lose (before I started strength training_ that I would get sweaty. Strength training still does not make me sweat and I'm visibly muscular. I'd only break a sweat if I was doing a quick circuit or in a hot gym. Also, some sweat more than others in general, like not everyone gets a red face etc.
Only thing I agree with is, that keeping her hair down has to be affecting the effort she can put in,whether it blocks her vision, strains her neck trying to keep it out of her face, or gets caught on the bench as she sits up and down on it - it's a nuisance