Haha aww. That's .. probably somewhat fair. Alex is like family to Chel, even though they'd drifted a bit recently. So, on the one hand, she's going to be thrilled that Alex is happy and has someone that treats him right .. and if/when she finds out who the boyfriend is, I'm sure she'd think Gabe is cute.
That said, Owen is basically Chel's other half, on a mostly platonic level. He's her rock and her savior - he's always been there for her, always chosen/protected her. And she will always choose/defend him. But where Alex is concerned, it's a balancing act, since she loves them both and she understands where each of them is coming from.
The tl;dr: Chel is glad Alex has someone who makes him happy, and she's likely to like Gabe whenever she learns who he is, so long as it's never directly in conflict with protecting Owen's heart.