I agree with **Seige’s ** and Muffin’s comments - even if you don’t plan on signing a pre-nup, it never hurts for the two of you to sit down with a lawyer, familiar with the family law of your jurisdiction, to give you a summary of what the law says. Informed consent is always better.
The discussion on this thread also highlights the need for a lawyer trained in your jurisdiction, rather than taking advice from people on a message board spanning different countries and continents. There is a lot of variation in how family law deals with matrimonial property, and the value of a pre-nup may vary considerably from jurisdiction to jurisdiction.
To illustrate, there are at least three different general models for family law: community of property; partnership in acquisitions; and separate property. In community, everything is held jointly unless the parties agree to exclude it, but in separation, nothing is joint unless the parties make it so. Partnership in acquisitions is in-between: the property that the parties have immediately prior to the marriage is not marital property, but what they acquire during the marriage is marital. And there can be a lot of tweaks and exceptions to these very broad strokes, like the status of the matrimonial home.
And there can be jurisdictions with more than one property regime. In Québec, for example, all three of the above are available. Partnership in acquisitions is the default, but the parties can opt for either community or separation.
You can see that in a jurisdiction with community property, a pre-nup has a lot more significance than a jurisdiction with separate property or the partnership of acquisitions.
And then there’s the example of bequests, which nashiitashii mentions - some jurisdictions may treat a bequest as non-marital property, even if made after the marriage; others may treat it as marital property, unless the testator clearly intended it to go to both parties. As well, some jurisdictions may use the date of death as the key date to determine if it’s marital property, while others might use the date the bequest is actually received.
I have no idea how nashiitashii’s jurisdiction treats these issues, and wouldn’t venture to express an opinion. But it highlights that if she wants to know her rights and obligations before going into the marriage, it doesn’t hurt for her and her fiancé to sit down with a lawyer.