I feel like Mangaka really overestimate the weight of swords and long swords. Even two-handed swords can be easily used in a single hand. The issue is muscle stamina. A few ounces can make a big difference after several strikes, parries, and even just holding it up. The only caveat is that anime swords tend to get several times larger than any real world sword. In this instance, I don't think that sword would have been throwing her around. She would have just been getting tired faster. Although, the Mangaka already introduced something about Beastmen having elevated combat ability, so nothing makes sense. This is just an excuse to get Caro a dagger. Mangaka preference.