At Ulala's command, Plusle and Minun abandoned Riolu and turned their attention to Froakie.
As it happened, Ulala had paid Froakie little mind at the start of the battle precisely because of the type matchup.
In her eyes, with two Electric-type Pokémon at her disposal, a Pokémon at a type disadvantage posed no threat at all.
But now, that had clearly been a miscalculation.
Electric-type moves did indeed deal double damage to Water-type Pokémon. There was no question about that. But Water-type attacks suffered no reduction against Electric types either-their power was delivered in full!
Even setting aside the disruption to their attacks, if they simply ignored Froakie and let it keep attacking like that, it would soon wear both Plusle and Minun down. They could no longer stand by and do nothing.
As for splitting her forces as Xia You and Lisia had, letting Plusle and Minun act independently to deal with their respective opponents...
Ulala neither wanted nor dared to do that.
After all, as most people knew, Plusle and Minun were Cheering Pokémon. They were better at fighting alongside other Pokémon. Making them fight alone not only wasted their distinctive strengths and Abilities, but also prevented them from bringing their full strength to bear. The losses simply outweighed the gains.
Thus, unless someone was particularly fond of them, only used them in Double Battles, or had a special need such as charging equipment, no one would readily send them out alone. Even without another Plusle or Minun as a partner, they would at least be paired with some other Pokémon.
And since Ulala had sent Plusle and Minun out together, she would never let them fight separately unless she had absolutely no other choice.
But in truth, these things had to be judged according to the circumstances.