I have seen so far that Jewelry Bonney can alter someone's age by touching them. So I'm just wondering how could you fight against that kind of power with Haki. Could Armament Haki defend the user from her power when she touches him?
There has been no proof of this yet, so I'm basing myself on Sugar's power and speculation. She has a similar power, where she can alter a person's body by touching them. We have seen Sugar turn a lot of Haki users into toys, so it is safe to say that Jewelry Bonny could also turn Haki users into babies.
But could they transform a Haki coated body? Well, Haki allows a user to touch the real person underneath, bypassing the Devil Fruit's power, so I would speculate that Haki would prevent someone from turning them into toys or babies, because the power would not be able to reach the victim.
Well, I guess you have to do it, like Zoro fought against Ain: Don't get touched.
The rest is guessing, because as far as I know, there hasn't been shown any other way to fight powers like hers so far.