When I was a kid, my dad had mostly horned cattle, and he sold lots of bulls to a large Montana rancher. This rancher wanted the horns left on them. I can remember this rancher taking as many as 25 bulls a year so we had lots of horns to train. We used to do this all the time. We just used a small saw and we would cut the top of the horn point off and it was amazing how much the horn would turn down. We also used to drill a small hole through the ends of each horn and tie chain across the animals forehead and secure it with wire through the hole in the horn. It only took a few weeks before the ends of the horns would be turning down. Once the end of the horn started to turn down we would take the chain off and the horn would continue to curve down. We also used lots and lots of horn weights over the years, and I still have several sets hanging in the barn.
Personally, I don't know why you would leave the horns on an animal but that is your decision. I have dehorned lots and lots of cattle over the years and to my knowledge I have not seen any that were any harder to handle after being dehorned. I guess there is always a chance this could happen, but I suspect your cow may have other temperament issues besides this.