I'd say it's like anywhere in London really. That doesn't really help, but my experience is that places like this, you have most demographics present depending on which street you walk down. For example, you have your paddy power with your drug dealers stood outside the door trying to peddle their gear, the next street over you have a new-build complex for £500k+ shoebox apartments occupied by professionals. In all my time wandering around Camden, I experienced both ends of the spectrum, but at no time did I feel unsafe, or consider taking off my Omega etc.
The cost of living in London is a very real and valid concern, I imagine she will have no option but shared housing, be it with friends, or privately, in which case there is the very real issue of dodgy landlords or just landlords who don't give a damn because there will always be a tenant waiting. The violence though, my experience is that while it is more of an issue than say, Bristol, it really is something that's been blown out of proportion by the press.