Ahhh.
Although, IDK if they're in-character.
Truthfully, I've procrastinated analyzing this matchup because lazy, but may as well do so now.
Pokedex information about Ralts that may be relevant:
Ruby | Ralts senses the emotions of people using the horns on its head. This Pokémon rarely appears before people. But when it does, it draws closer if it senses that the person has a positive disposition. |
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Sapphire | Ralts has the ability to sense the emotions of people. If its trainer is in a cheerful mood, this Pokémon grows cheerful and joyous in the same way. |
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Emerald | A Ralts has the power to sense the emotions of people and Pokémon with the horns on its head. It takes cover if it senses any hostility. |
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FireRed/LeafGreen | It is highly attuned to the emotions of people and Pokémon. It hides if it senses hostility. |
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Platinum | If its horns capture the warm feelings of people or Pokémon, its body warms up slightly. |
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Legends: Arceus | Tends to prefer people with a chipper disposition to those who are gloomy, but it has shown no discrimination with regard to age or gender. Needs more research. |
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Scarlet | The horns on its head provide a strong power that enables it to sense people’s emotions. |
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Honestly, underdetailed compared to the rest of its evolutionary line. Favoritism much, developers?
Anyway, this brings up the question of: What is Penny's disposition like?
Also, IIRC, SBA gives combatants mutual hostility, which, if so, would mean Ralts would be inclined to hide from her, despite being hostile, so it'd probably try to fight remotely, or keep distance between the two of them.
Telekinesis & Teleportation are especially helpful for this.