I also had no idea Ranka would actually show up on the planet; I thought we'd just get shots of her being depressed, a big fight, and, as you put, "SherylxAlto fluff." Now that I look back at it, the writers never hinted at Ranka riding along in Michel's modified fighter, so when she showed up, I was completely caught off guard. In a good way.
I really thought she'd learn to be more assertive after ep. 11, but I didn't expect *this*, and I must say I was pleasantly surprised!