Ran like mad to get someone to destroy the Gensokyo-destroying meteor? Nobody clued her in to this plan.
Late response is late, but I thought she was running in because of the situation about the SDM demanding humans for food. Marisa blasted off at the speed of light but poor Keine had to take the ground route and only just arrive (and also to spot the exploding disintegrating meteor). Marisa was essentially telling her she took care of that situation.
