That's the wisdom of experience speaking! She might be older and stronger than Maria, but she's only been tapped into her destiny for about a day. Say, maybe that's why she hasn't been able to use her powers, because she's been too close to Hiroshi? Should she get rid of him?

"Is that the only problem? Humans are one thing, but if it comes down to a fight between witches, Venus won't lose! As long as I have love and beauty on my side, I'm invincible!"

...Nah, she draws her powers from love, of course, killing Hiroshi wouldn't help at all. And she should be focusing on getting rid of the real problems around here.