If Aglae is Lila her plan this ep was genius. She knows Alix is Bunnyx (because it was announced to the class when she was there) and suspects Marinette is Ladybug. So she guilttrips Marinette about Alix's birthday knowing that if she is Ladybug the predictable move would be for her to relieve Alix for one day so she can celebrate it. Low and behold, the next day Alix showed up for her birthday and Marinette is nowhere to be found and Alya immediately gets an excuse text the second Aglae/Lila gets people wondering where she is (which is exactly what she'd do if she was observing the party from the Burrow) Now she's almost positive but to be 100 percent sure she starts and Akuma attack, if Ladybug showed up fused with the Rabbit then it's a certainty, but this one Marinette doesn't inadvertently fall for and doesn't bring the rabbit into battle which means that while Lila is certain Marinette subbed for Alix, that doesn't necesserily mean she's Ladybug because Ladybug showed up sans Rabbit, meaning it's possible Ladybug is someone else who roped Marinette into helping.