I have to play (and improvise) a 50 year old female anorexic, who is a software development manager, in an acting job; any tips on good lines or personality traits?

While I am not an actor, I do know something about eating disorders. Here is a link that describes in detail the symptoms of anorexia that might help. http://www.lifeworkscommunity.com/news/blog-wordpress/88/

I realize that you may be looking for some very specific - and easily applicable information about middle-aged anorexic female software developers. I can't provide that. However, in my experience a few hours of research goes a long way - especially when you are trying to create a character from an environment which is unfamiliar to you. People watching 'in the field' and various documentaries or clips you can find online can all serve to ignite your imagination. Search for some key words on Google and Youtube and see what you find. In your case I would also skim a couple of tech blogs such as http://www.techcrunch.com. You might find some phrases you can use or some interesting women that you can then look for on Youtube. You may not be able to find any anorexic 50 year old tech women that you can just copy - you probably need to look for those elements separately and then combine them yourself in your character; what's her story and what's it like to live her life, what  motivates her to be 'slightly nasty' etc.? Being as specific as you can will help you in your character portrayal - however, since you are all improvising, your ideas about her can't be completely set in stone. You need to be open to the inputs of the other actors when you are playing - and they might say or do something which means that you have to adjust your story.   Once you've done a bit of research you should also have some ideas as to how you might change your physicality - your mannerisms and the way you generally carry yourself - without going overboard and becoming a caricature, of course. To make the character believable it's very useful to have a clear objective - what do they really want? Once you know what your character wants you can focus on the other players and how to change them when you are playing the actual scenes. Focusing on your fellow players will help make your performance more alive and less 'actory' and introverted.