The fact you said "in order to get her here quickly" makes me think you might be thinking of AOS on a tourist visa. This is fraud. There is no loophole if you already have immigrant intent.
But let's say I misinterpreted you, and you only want to get her a visitor visa in order to just visit you in US.
You said she never left the country, so I'm thinking she never had a US visa, correct? So that would be her first time ever applying for an American visa. Right now, waiting times for a visitor visa in Brazil are at 400 days or more. And it's 2 days of interviews now from accounts I heard. You can try speeding it up by constantly checking the website to see if earlier dates opened, but it's luck. Some despachantes (visa agents) promise you to get it quickly but I can't attest to that.
Just another perspective. I am on day 436 waiting for my K1 petition to be approved, only planning on being in US by October now. My US tourist visa expired a few months before I applied for K1. I won't even risk renewing it because I am pretty sure it will be a waste of time and $160 (it's almost R$900 here) because I have immigrant intent and have weak ties to my country. I'm young, have an American fiancé, work from home and live with my parents. I have travelled abroad a couple of times and have a tourist visa/work permit from Canada, and I am 99% sure they will deny my renewal (note that there isn't an interview in my case for renewals, I still won't risk it).
Her being young, recently graduated, with an American fiancé and living with her parents is a bad sign. When I first got my visitor visa I was also young and going through university, I was also going to travel with my parents, we went to Disney World. The officer gave me a hard time but in the end approved my visa. I don't think this will happen nowadays. The letter you intend to have her present won't mean much to the officer, same as her having crochet business or you being a soldier.
You say you intend to get marry in Brazil. Can't get married in Brazil on a K1. But if you do it, apply for a spouse visa. And wait. And wait. And in-between, visit in other countries or come visit her in Brazil, forget about her in US before the spousal visa is in hands. I met my fiancé 2 times in Mexico, but your fiancé will need a visa to enter Mexico though if she doesn't have a US/Canada one. Maybe think of other countries you both can go and is easier for her to enter. We don't need a visa to enter many countries in Europe.
Just my two cents being from Brazil, but do listen to all experienced users here on this thread.