Love me, but don't interfere with my wallet

My fiancée has been constantly commenting on how I've been spending my salary lately. She suggested opening a joint account before the wedding, but honestly, I found it a bit early. I have my own job, my own money; I don't understand why she's doing this. I don't think there's anything that damages relationships as much as finances. Do you think this wedding preparation stress will turn into a bigger issue later on? How should I set a boundary?