The Excalibur wash for geldings and studs "Semi Annual Weenie Wash Day" works great for udder smegma too.
Once you get the smegma off, you can just use a baby wipe weekly to polish up her tatas. =)
Draftrider that's brilliant! I don't know why I never thought about baby wipes before. You have just made this ole gals day! I imagine, with the scentless wipes that I buy for my granddaughter, I can also use them on my gelding for "touch-ups".