those settings are pretty low but since hair is coarse, you’re getting results. the finer the hair gets, the harder it will be to get those hairs at those settings. if you’re getting burns even from those, i would definitely consider switching to a Yag like a Coolglide like you said. For this area with coarse hair, it should work just as well with an experienced tech, but not cause burns this easily.
not sure what you mean by “you know that hair wasn’t touched by laser because it grows back a few days after treatment” because hair always ‘looks’ likes it’s growing in for 2 weeks post treatment and then sheds. do you mean to say that it doesn’t shed like the rest within 2-3 weeks at all? if that’s the case, she is not treating the area, so you should point it out and make sure she does next time. But if I were you, I would go with a Yag to avoid any burns.