Well, suit pants for girls are usually even less helpful when actually carrying something in there than guy's dress pants I'd probably choose either a Spyderco Grasshopper, Kiwi or a classic Victorinox Pioneer Alox. All three very classy looking and yet small/slim enough and practical. The Spyderco Squeak would work nicely too since it's very compact and light-weight.
SAK. Either my Super Tinker or Pioneer Alox. Generally prefer the Tinker, as the need for scissors seems to come up more often in those settings. For example, trimming loose threads, cutting small string/ribbon, etc., and especially if those things are attached to a person. The classic red plastic handles may not be "classy", but they are familiar to everyone and don't make most observers uncomfortable.
say brother, as others have pointed out here, suit pants pockets are pretty poor for carrying things. you may want to look at a sak secretary-- a very nice functional pen knife that should work great with formal clothing.
my best of wishes to you for whatever you may finally decide on!
I asked something similar here, and one of the answers was so good, I have to repeat it.
Carry a Cold Steel XL Espada. Nobody will say a word.
A little further on was an observation that people are very polite to somebody with a katana.
Gerber makes the Ridge, a nice little framelock that can double as a money clip. Likewise, the similar size K.I.S.S., P.E.C.K., and H.U.G. by Columbia River. I picked up a Kershaw Crown II to add to my "polite knife" choices, because I like one-handers and black micarta. This is in addition to the thirty or so suggestions that have already been made, of course. My suggestion would be to get one of each of everything, but I like little knives.