There's your answer. She pregnant with hormone swing while worrying about the baby's financial needs. She loves you and gave you the OK to get another bike but yet she probably have other worries in her mind. The kids need a daddy but yet the daddy is out getting a roadbike. Her mindset is thinking that roadbike translate to faster speed and more chances of injuries. I bet that spike her hormones level.

Suggestion. Like someone else already mention, better to ask for forgiveness then permission. Get it first and don't tell her the real price if you can get away with it. Yes she'll have her suspicion, but she'll most forget it if she see how happy you are with your purchase. Just beware though, all good things comes with a price, you might have to be a "Honey Do" for a short period.