To be perfectly honest, when it happened I didn't catch it at all. It was only later when reading about it that I learned about it. It was subtile to get it pass the censors, I guess, but as a young girl who was very into girls, you'd think I'd pick up on it. I did notice the chemistry of Batgirl and Supergirl though. People talk about that less than Harley and Ivy, but it's there. Maybe you're right. I dislike Harley so much, and am not into red-hair, that it just probably blew pass me. BUT then again, Babs is a ginger, so I guess that doesn't answer that...
I like tat DC has kept Supergirl and Batgirl friends and never had them become enemies like Bats and Supes. I haven't been that into DC or Marvel in years, so I only realized Ivy and Harley were a thing when I saw the clips from the episodes when they were together. Though it did seem that for a bit DC went lesbian crazy with Harley as they also had her interested in Powergirl, which I can't blame her for that, but seemed like an odd thing.