Unfortunately the new way of mapping gets me an inside out object often (ALWAYS PREVIEW YOUR SCULPTS BEFORE UPLOADING! Even if you don't upload them through SL's interface), which means the image needs to be flipped horozontal in post. SL just sometimes get confused what's an inside and what's an outside, since it only textures on one side of the face. (Of course, say you want an inside out texture for a bottle or balloon or something, flip a right side out sculpt map horozontal to get it inside out.)
Mirroring the actual object can be done in Blender as well- ctrl-alt-M if I recall correctly. However it can also be done in post! Assuming you have an image editor that divides up the colour channels, invert the red channel (note: this mirrors on the x axis. Invert one of the other channels to mirror along their axes instead), and then flip the whole thing horozontal (this is to make it not be inside out, and assumes that the before copy wasn't inside out either- to un-inside out something, flip the whole thing horozontal). If your sculpt is inside out, flip it back horozontal.