Lana's had decent supporting roles every now and then. SM31 wasn't focused on her, but she and Popplio still got to help out with the Wailmer. SM22 wasn't focused on her, but Popplio was still integral to finding Pallossand's shovel.
I have a feeling this is exactly what you were driving at, but Lana's problem is that she's hindered by her specialty type in a way that Misty wasn't. She can't/doesn't really do much outside of episodes in an aquatic setting. You can even see that in her focus episodes. Aside from SM32 (where everyone got some focus anyway), every single one of her focus episodes were set in and around the water. And it doesn't help that while Popplio doesn't quite have Goldeen/Horsea syndrome in that it's completely useless on land, it is by far the most aquatic Water starter yet and the least mobile on land. She needs a Water type that's more mobile on land than Popplio, otherwise she'll continue to be useless outside of episodes with aquatic settings. That's another point for Dewpider/Araquanid being her second capture. Bonus points if the writers actually play into this, and Popplio develops jealousy toward Dewpider/Araquanid because they get used more often due to being more mobile on land. Extra bonus points if Popplio has evolved by then, because as a Brionne, it would hide the jealousy from Lana.
Otherwise, I pretty much agree with the rest of your post. We're kind of getting off-topic here, though. I don't think the girls are going to do much in this episode and wouldn't be surprised if this was like SM16 where most of the focus was on Pikachu and Poiple.