Booking German trains without a credit card

she is Australian so can't use her passport

Why not? A passport is essential ID for a foreign visitor.

When I use Bahn.de I get a choice for ticket identification. The options include a travel document number, such as a passport number, linking person to the name on ticket. This is your sister's best (only?) alternative.

A debit card would be irrelevant and of no value.

She does have a Mastercard debit card, but I'm not sure this counts, does it?

If it's anything like my Mastercard debit card, it DOES count. I live in Israel, and my Israeli Mastercard works as a debit card in Israel and a credit card abroad. I have used it to book all kinds of things online in various European countries without any difficulty.

When I booked a flight online (UK website) I attempted to type my card number in the box for debit card. It didn't work (presumably because it's not a UK debit card). I then put my card number - same number, obviously - in the box for credit card and it worked fine.

But it might be worth contacting the bank in Australia to make sure.

Do you mean debit card for payment (not for independent ID)? If she can debit pay, or use it as a CC then the means of payment ought to be OK. But the .. use as CC .. that's the same point again.

the website seems to require her to have one (CC ) as a form of ID?

What they want to see, as an acceptable form of ID, is the card that was used to make the payment.

I just checked bahn.de for the ID question. From a pull-down list they only have a few countries that issue ID cards, in other words not Australia with passport as option. So that explains
> she is Australian so can't use her passport

Direct debit payment is only possible under certain circumstances, which do not seem to apply in this situation.

I will browse a bit further and see if I can find some positive news.

Registering and then logging into the bahn.de site claims to give a person the privilege to buy tickets for someone else.

It is also possible to pay with direct debit if registered (that is, CC not required).

However, I am myself not registered, so do not know if there are further country-of-residence or other restrictions on this possibility, or what the ID implications will be for the ticket-holder if someone else buys the ticket.

For a Bahn online ticket to be considered valid, it must be combined with some form of individual ID which contains a numerical code (codes containing both numbers and letters are not accepted due to technical reasons) which is also entered when booking the ticket; the ticket controller in the train will check both the printout of the ticket (or the QR code in an MMS on a phone if it's a mobile phone ticket) and the ID - otherwise, several people could travel on multiple copies of the same ticket.

This what the German version of the bahn.de website says about ID options for this purpose:

BahnCard (preliminary BahnCards not accepted), bahn.bonus Card
Kreditkarte (credit cards:) (American Express, MasterCard, Diners Club, Visa oder JCB)
ec-Karte/Maestro
Personalausweis (= national ID cards from a limited number of countries - not applicabable for Australia)

Hinweis: Reisepässe sind als Identifikationskarten nicht zugelassen. (Passports are not accepted)

(I think this is because their codes combine numbers and letters)

Based on that, I would assume that both a Maestro card and a Mastercard would be acceptable forms of ID; as they are only used to validate the ticket and not for payment purposes I doubt that it will be relevant if they are credit or debit cards, but you could call Bahn's international ticket service at + 49 1805 - 996633 to double-check.

The important thing is to enter the type of ID and its number correctly when the ticket is booked - if the user is registered, the card used to pay for it can be different from the one used as ID, as mentioned by BthDth.

Otherwise, if the savings fares (Sparpreis tickets) are already sold out, your sister can wait until she is in the country to buy her point-to-point tickets in traditional paper form, either from a counter (if it's a large station) or a machine, ditto for Laender Tickets, Schoenes-Wochenende-Tickets and Quer-durchs-Land-Tickets as their prices are fixed and no discounts offered for early buyers. There's also the possibility to buy tickets at Bahn agencies abroad - there's a list on the website.

Unless she has to book in advance, why can't she just purchase them on the kosiks in the train stations? I've done that with my mastercard debit card and it worked perfectly fine.

Booking in advance only gives a little bit of benefit with price reduction. Honestly, unless its on a weekend the train should not be sold out. And if it is... trains in Germany are excellent - many hourly, 2-hourly, etc.