Its okay to be concerned, and asking your friend if there should be any concerns about your safety prior to your visit should not put her off. Every Brasilian, rich middle-class or poor is affected in someway or another by the violence which is prevalent throughout the country. Just every Brazilian has a different attitude towards their safety depending on their own situation. Some are very paranoid, most cautious, and some just don't care.
It is true that Salvador and most of the cities in Brasil's northeast are dangerous, many made the lower 25's on last years list of the world's most violent cities: http://www.businessinsider.com/the-50-most-violent-cities-in-the-world-2015-1?op=1
However, thousands of tourists visit Salvador each year and the majority return safe with good memories. I've lived and traveled extensively throughout Brasil and trusted my well being to complete strangers, some I met along my journeys and others I knew in advance from the Internet. From my experiences most people are good natured and will lookout for your best interest, but as a gringo you will come across some who seek to take advantage of you, or lack good personal judgement determining how to keep you safe-r.
What will keep you safer is having the right attitude towards your safety, being aware at all times of your surroundings, of your friends judgement, the people who she associates with, maintain a low profile, and do your research ahead of time about the areas where she lives, and where she will be taking you to.
If your friend has spent anytime living abroad in the United States, Canada, Western Europe, Australia, etc then she will understand thru her own experiences the differences you will be faced with when you arrive. If has not, but she comes from a middle to upper class family she will still understand this and tell you there are just certain ways to behave, and places not to go for your own safety.
A personal experience i'll share with you, I first went to Brasil straight out of College to meet a girl I had been talking to over iCQ for 2 years . We talked almost daily with each other, and when I planned to go visit her, I wanted to have my own space so I asked her to set me up with an apartment in a safe neighborhood in Rio.
A few weeks prior to my visit I began chatting with another woman I met through a website dedicated to Rock in Rio, and when she inquired which neighborhood I would be staying in and where, she strongly advised against it as the area was not safe. Additionally she warned me that my friend comes from a poorer area of Rio, and her judgement of what is considered safe may not be in my best interests.
I didn't listen to her, and in the first month I was robbed in broad daylight returning from grocery shopping, and a week later I was assaulted and robbed in the elevator of the condominium I staying in.
The women I had known for 2 years refused to go with me to the tourist police station because it would mean a 2-1/2 hr bus ride during rush hour from the area in the burbs where she lives.
When I told the girl I had met off the Rock & Rio website, her mother drove her from Niteroi to pick me up without telling me, then took me to the tourist police station to file a report, and then told me to gather my belongings as i'm going to spend the remaining 2 months of my trip staying with them.
I had a wonderful time living with her family, they took me shopping and bought me new clothing to dress down, showed me how walk the carioca way, how to act while i'm out on the street, how to react if we get robbed at any-point, and most importantly how to have fun while being out. I later hooked up with this girl, and we are about to celebrate 14 happy years of marriage.
After I moved out of the apartment, some thugs broke into and ransacked the place in the middle of the night. A week before I left Brasil a german tourist was thrown out the window a few stories above my apartment by a pimp. It was a really bad area of Copacabana. I was also ripped off and over paid for the suite by almost $500 reais.
My wife and I have both been robbed together while in Brasil, but everyone else on the bus was robbed too. After living sometime here it becomes second nature how to react, and to always look over your shoulder, keep an out for the dark places ahead while walking on the street at night were the pievte's (street kids) kids or thugs sleep or hide to ambush you.
One advantage you have over my first visit, was social network didn't exist back then, so you can do a lot of research about herself, her friends, facebook groups about the area of two she lives in where they report muggings, violence to get an idea what you are entering into.
Instead of asking your friend how you said it in your post, I would ask her what she recommends to keep you safe while having fun during your visit.
Also, there are plenty of white Brasilians who could appear to you as being a gringo. It's all about how your present yourself. Feel free to ask any further questions and if I don't hear from you I wish you bon voyage.