Since we know that Sonia was a Pokemon trainer with Leon before she decided to step back from the Champion’s Lifestyle, and even fought in a few tournaments, it was likely that she was very good at battling with and training Pokemon. However, we never see her skills in any media from the anime, to the games, to the manga. Plus, the only Pokemon she really owns is Yamper. We can make some assumptions and some fans have even put together what her ideal roster of Pokemon would look like, but we will never really know the extent of her skills. Maybe in the future, we will see her whip out some poke balls and do battle with some enemies to show off what she can do, but for now, all we can do is guess.