First and foremost, congrats on your internship at Bayview! I work at JHU (Homewood; the main university campus in the Charles Village are) and have live here for about 5 years after growing up in fairly rural/suburban surroundings. So I was, like you, scared to death when I saw what I was getting myself into. Crime should be a big concern. While this city does change frequently, sometimes block to block, there are neighborhoods considered safe. HOWEVER do keep in mind you are in fairly dangerous city and you should always pay close attention to your surroundings. A lot of the crime that does happen here is because people get careless, forgetful or act like they don’t know what they are doing and these are the people who will be targeted because, I believe, criminals view these people as either tourists or students; both of whom are considered easy targets.
Park Ave. in Mt. Vernon should be a fairly safe bet; Mt. Vernon is predominantly a club, bar, restaurant area with some nice museums, festivals, etc. Again, without knowing the exact location, sometimes Baltimore can vary block to block. From what I know, as for Park Ave, stay within Mt. Royal, Eutaw, North Ave., Preston, Howard. Charles Village, including the Marylander, St. Paul and W. University Pkwy, are fine and a step away from the shuttle (Park Ave you may need to walk thru some sketcher places at night to get to the shuttle). Lots of students, including those at Bayview and the med school, live around here. Again, stay in the boundaries of 29th, maybe 28th street, Barclay (though I would suggest staying the closest in to campus the better—it gets sketcher as you move east), and Remington. Really nothing too bad further north. Some other around Charles Village could be Hampden. Wouldn’t suggest nearby Waverly as it is very touch and go even though I know plenty of people who have lived there and they have been fine. Canton is good but I agree with the other poster that nighttime may be an issue, but a lot of areas have more prevalent problems at night. I have friends who live in Fells Point and walk to the med campus to take the shuttle, but walking from the med school at night is not safe but Fells can be a fun community, abet filled with loud partiers (as Canton is also inclined to be). Take a look in the JHU gazette for sublets or shared apts.
http://www.jhu.edu/~gazette/ or the jhu housing site http://www.jhu.edu/hds/offcampus/apartments/charles_village/charles_village.htm (broken link). Stay somewhere within walking distance of the shuttle since our public transportation is less than desirable (and do NOT under any means take the “subway” or “metro” or whatever they call it here).
Since the police/government do not like really putting all the issues out in public, the best crime fighting tool we have is the Baltimore Crime blog
http://baltimorecrime.blogspot.com/ which compiles much of the serious crime that happens everyday from all the sources that list it somewhere. Don’t let it scare you too much, but use it to see if any areas you are looking at have had any serious problems lately (more so if you have exact street addresses as, I’ve said before, this place can really vary block to block). And I liken the City Paper’s Murder Ink Maps which plot our daily murders http://www.citypaper.com/news/murdermap.asp?year=2007 (broken link). Lovely that we have to think of this, huh?
As for paying attention to your surroundings… I see some many undergrads listening to their ipods or talking on their phones, oblivious to the world around them. DO NOT DO THAT. A dear friend of mine, who is built like a football player and old enough to know better, got mugged because he was listening to his new ipod rather than paying attention. He no longer has that ipod nor his wallet nor his wedding band, but luckily is safe and sound. As for your comments about being small— size obviously does not matter in Baltimore as you can see

. As in any city, especially here, if you must walk without your friends, walk speedily with confidence (like you know where you are going), hold your purse/bags tight, keep your keys in hand, keep thinking and you will probably be fine. If someone talks to you, consider just saying “sorry” and moving on without batting an eye; most likely (and not to sound like a pessimist but you have got to be one to survive sometimes) they want money or are attempting to scam you. Most people here will ignore them and you can to; no need to be friendly to everybody! If they really bother you, tell them you will be happy to call the cops for them (just don’t pull out your phone there or be distracted in anyway). It has worked for me a number of times. And as a JHU staff member, you can always ask for an escort by campus security if you are on any campus or live around Homewood (http://www.jhu.edu/~security/) (broken link). As pessimistic as this sounded, I really hope you come and see what IS so lovely about this “charming” city; its food, its social life, its arts, its unique characters, its location. I now really like the city once I learned where to go and where not to go and have not had any problems myself. If you take away the crime, many of us would never leave… Welcome to Baltimore “Hon”!