OK Marie....So this wasnt your friendliest welcome to a gun forum. Unlike others, I will assume you have the knowledge of using a gun safely and proficiently. If you don't, please take the advice from some of the others and find someone who can familiarize yourself with them before looking into buying one. This can be either formal training or informal, but make sure its with someone who knows their stuff, many gun stores will have information on affordable concealed weapon classes in your area.
As for the weapon itself, where I understand the need for concealment in your situation, dont get something based solely on that. Get a gun that will do what is intended and figure out how you are going to carry it, then dress accordingly. As far as your purse, most no-gooders will not wait for you to dig your pistol from your purse. Get a purse designed for this that will allow ready access in a hurry if needed.
Where the cartridge is concerned, you need to figure out what your recoil threshold is..my fiance is 5'4" tall and weighs 135 , and has no problem shooting a colt commander in .45acp, and I have talked to at least one large man who said a 9mm kicked too hard..Recoil is NOT a standard thing, some people can handle more or less than others. The best thing to do is test fire a few different models and different calibers and get the largest caliber you are comfortable with shooting. A .380 will do the job if need be, but if you can handle a 9mm, .40, or .45, get on of those. The point of armed engagement is to neutralize whatver is threatening you in as short of time as possible. a revolver should not be ruled out either as they are inherantly more reliable and simpler to operate, but your caliber choices are more limited.
Do not let the gun store proprieter tell you what you need. Stay away from any Jennings, bryco, davis or raven names, these pistols are of low quality and will not be reliable.
Practice Practice Practice...Shoot it and clean it as often as time and budget will allow. Dont get the gun and let it sink to the bottom of your purse forgotten until the moment you need it. Again, the name of the game is instant incapacitation of the threat, and the more you practice, the better the chance of you getting rounds on the target before something bad happens.
Its unfortunate that we live in a world where we require firearms for self defense, but I thank god we live in a country that allows us to do so, for the forseeable future at least.
Good luck and I hope that helped some...