Aha, more information. This is a horse of a different color.
A prior marriage without a decree of nullity means you cannot marry this person until and unless hse is declared free to marry. She will have to have the marriage examined for nullity by the Tribunal **before **you can be married.
There are some other options when one or both persons were unbaptized. In the case of the unbaptized ther are also options for dissolution of the bond. This chart is a good summary:
diocs.org/Portals/1/Documents/Tribunal/Decision_matrix.pdf
But, now that you’ve included this information the advice is to make an appointment with your priest
as soon as possible. Whether she becomes Catholic or remains protestant, you cannot marry her unless she is declared free to marry by the Church. She has a prior bond right now. There will need to be a thorough investigation including baptismal status, any prior marriages of her ex, etc.
Go see the priest together and take it one step at a time.