I think you're hiccup is going to be finding a single holster for both IWB & OWB. You can purchase wonderful holsters for each method of carry, but to find one holster that does both well may be asking a little too much. This is especially true if the holster is for a woman.
Depending upon your girlfriend's physique, you may consider purchasing a holster made specifically for women. Women with shorter torsos, wide hips, narrow waists, large busts, and/or any combination of these factors often report problems with traditional holsters that were designed with men in mind.
Tucker makes some excellent revolver holsters, and I'm sure they could adjust any of their designs if necessary:
http://rlcompanyusa.stores.yahoo.net/reho1.html
Kramer makes what are reported to be very nice holsters designed specifically for women:
http://www.kramerleather.com/products.cfm?categoryID=22
None of these holsters are cheap. If you're looking for something less expensive you may consider this Galco Speed Paddle holster. It can be purchased for under $60 with free shipping here:
http://www.opticsplanet.net/galco-speed-paddle-holster-for-ruger-lcr-right-hand.html
A paddle holster can be very convenient, but some women complain that the gun rides too high or is difficult to draw because of the way their hips cant the gun.
Holsters are often a process of trial & error. Do your research first and hopefully it'll reduce the number of errors.