how does one get a credit rating?

issue bought up this week.

21 year old stepdaughter wants to upgrade her car as current one is unreliable (keeps breaking down). she has plenty of cash in the bank but is looking at moving out of home end of the year so doesn't want to spend more than half.

means she needs to get a loan for the balance. problem is, she's been knocked back because she has no credit rating (by the bank where she has her $10k+). the only place to offer her a loan will only do so if we go guarantor. this doesn't suit us as we're looking to borrow later in the year - but we are more than happy to lend her the money ourselves and she can pay us back over 2 years interest free.

but she's going to have this problem again in the future - how does she get a credit rating?

she pays prepaid for the mobile and doesn't have any credit cards. i suggested she get a credit card and use it slightly and pay it off straight away - but surely there must be an easier way.
get a credit card / store card.
get bils (ie, elec, gas) in her own name.

I am still a little surprised she cann't get a loan - the lack of credit history usually isn't a huge barrier to this. I am assuming she has regular income - is it full-time? part-time? or casual?

If she is casual, this may be a huge problem, at least it has been for me. I wasn't even able to sign up for a $19 month capped mobile phone contract - because of my casual status - despite having the job for 4 yrs, they didn't even want to know my income details.
A family friend told me when I was applying for my PPOR 10 years ago that I'd never get a mortgage because I had no credit history. Never had a credit card, personal loan etc. but was glad to prove her wrong, it was a complete non-issue. However, I did have a mobile phone on a plan, so not sure if that was the difference, that and the fact I was applying for a mortgage so I guess it was a secured loan vs. a car loan. And it was a long time ago (feels like yesterday), so maybe things have tightened up.

I was also a casual at the time, when I say casual, I was paid by the hour, but working full time hours (the days when I was too quiet, naive and let my boss take advantage of me - thankfully I grew up and moved on). Again this wasn't an issue for me, I just had to get the bank a letter from my employer stating that I worked those hours on a regular basis.
Usually personal loans arent that fussy because they will take a bill of sal over the vehicle.

While its poss that she did not have a credit per period, that alone isnt usually the reason for a decline.