Why not watch openly if you're so interested?

"You guys really have the guts to come along, huh?" Angel's cold laugh was visibly dangerous, the threat in her eyes clear to any sane person.

Isabella, however, seemed unfazed as always. Each time she faced the temperamental heiress, she seemed to have her own unique way of handling it. 

"Hmm? What was that, Angel? I didn't quite catch that. Aren't we leaving now? It takes about an hour to get to the swimming venue, right?"

Angel was blunt. "Can't you go by yourselves? Contacting my boyfriend to have me drive you all seems a bit underhanded, don't you think?" 

Hearing Angel call someone else underhanded was quite novel.

Isabella blinked. "Oh, that wasn't really the intention. I just thought since we're all club members, moving together would foster unity, don't you think? Of course, if Angel isn't up for it, the three of us can go on our own."