A reciprocal agreement in the UK means a UK Court can enforce a CCJ (County Court Judgment) using the legal system of the other country. If there is no such agreement in place, a creditor can sell a debt to an agency in the relevant country and debt recovery procedures will commence under the law of that land.
Has she got everything in place to emigrate? It is hard enough to get in to Australia without being insolvent
Unless it is a student loan debt, then if you live abroad for a minimum amount of time (think 5 years) they write it off. Otherwise debt will follow you all over this world and even into the next.