On the face of it, the property is in her name, so the onus is on you to seek an order from the court to establish your interest in the property and to correct the title records.
Depending on your circumstances you may be covered by the Family Law Act, state legislation for de facto couples, or the common law, but regardless, if you can show that you paid for the property, either completely or partially, it is very likely that you could successfully apply to the court to have your interest in the property declared and the title amended accordingly.
However, you will need to act promptly and the nature of the law is somewhat complex so this is a matte where you would be foolish to try to resolve the matter without the assistance of a lawyer to represent you before the court.
Hopefully, if you engage a lawyer, they will be able to pursuade your ex that she is not entitled to simply claim the whole property and you can then try to negotiate a satisfactory resolution without recourse to actual court proceedings, but your ex's attitude is likely to only improve if faced with form legal advice that you have a valid claim on the property.
I trust the above assists.
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