Answer:
exchange her British currency for Canadian currency
Step-by-step explanation:
When in a foreign country, the legal tender, that is the means of exchange is with the currency of the country where you are.
So Sarah cannot use her british pounds in canada to make payments for goods and services. Given that the pounds is not the recognized currency of transactions in Canada. She has to exchange her pounds for Canadian currency first, before she can buy this item for her sister.