Make sure she is on the electoral register, with her salary paid directly into her bank account.
Have any regular payments made from the account by direct debit.
To build up a credit history for free; take out a credit card, spending on it each month and clearing the balance each month.
Credit card, with balance paid off every month = very good credit rating
Credit card, with at least the minimum paid each month (ideally more) = good credit rating
Credit card, with no minimum payment made = bad credit rating
I would not bother to take out a loan (paying interest) just to get a credit rating, when other options are available.