She has almost certainly been described as intense. Said admiringly, nervously, occasionally as an explanation for why someone felt uncomfortable. All of those versions describe an effect. The quality underneath is more specific: she can see in the dark.
Fixed water. Pluto-ruled. Still water, not churning. The bottom is visible. Her stillness is not passivity. It is depth, the mechanism by which she perceives what is not visible at the surface.
She knows things she was not told. Picks up the gap between what is said and what is true. Not a skill she developed. Something she has been doing since childhood. People feel seen by her in a way that is sometimes uncomfortable, because being seen that completely requires doing the same in return.
She understands what is actually driving behavior. The fear behind the anger. The pattern underneath the surface event. She has been somewhere internal that not everyone can access, and she knows the difference between discomfort that is passing through and discomfort pointing at something real.
In relationships: all the way in. Wants the same in return. When she trusts someone, the loyalty is remarkable. When the trust breaks, the withdrawal is equally complete. Rarely gradual. She is either in or she is out.
Intensity becoming control — the need to see clearly becoming the need to manage everything knowable, holding the people she loves in a grip that does not let them be unknown to her — that is the shadow.
She does not need to see all the way to the bottom of someone to trust them.
Her willingness to go where other signs stop is not a character flaw performing as virtue. It is what allows her to be present in the places other people leave.