The first time Caroline sees Damon with Andie Star at the Grill, she knows instantly that the woman is under compulsion. Taking away the fact that she's a vampire and she almost has a sense for compulsion when it's in use, she recognizes the signs.
Maybe the signature left with the human is different with other vampires or maybe it's just a similar modus operandi of Damon's. Maybe it's the mysterious glint she catches in Damon's eyes, like he's playing puppet master—seeing it again, she remembers that look and shivers at the memories. It could be any of these really, but Caroline suspects it's the striking similarities between the way Caroline remembers acting and the way Andie is portraying herself.
The constant talking, the way she shuts up as soon as Damon looks at her a certain way, the very faint tinge of fear in her eyes that blinks away faster than any human could register. The way she smiles at him and asks questions any person with full control over their mind would never ask.
Caroline doesn't stay at the Grill long. She can't stomach the sight.
A part of her feels bad for Andie because she knows what it's like to lose a part of yourself to Damon Salvatore and not even remember doing it. And a part of her is extremely jealous because once upon a time it was her, and in a way, she misses that. How sick is that?