From what I could tell(can't speak Japanese), Serena tried to console Ash by telling him about how she got back on her feet after losing pokemon showcases in the past. Ash basically said that she has no idea how he feels while raising his voice at her(or something to that effect.) And then Serena gets frustrated and throws snowballs at him, mentioning something about how the ash she likes is energetic, etc. Then she runs away.