If you want a desensitizing lube, I'd recommend Adam & Eve's Ultimate Anal Lube. It uses Lidocaine instead of Benzocaine, which is what most desensitizing lube's use. It numbs just enough for comfort, but not enough so that you can't feel anything. You can get it and wide variety of other lubes at www.adameve.com Good luck.
I'm a huge astroglide fan, it stays slippery, unlike ky and other jelly-ish lubes. but wow, that adam and eve stuff sounds rather nice, i may check it out. (hee hee, ass-troglide)
If you use a desensatising lube, You might do damage to her and she won't know it until after the affects of the lube wear off. Spit works great, hehe.
WD-40.. It works wonders! WD-40 is the #1 multi-purpose problem solver.. It cleans, protects, penetrates, and lubricates!!
Mobil 1 Synthetic Grease is an NLGI No 2 high-performance grease which combines a synthetic base fluid with a lithium complex soap thickener. The thickener system provides a high dropping point, while additives impart optimum extreme-pressure properties and excellent resistance to water wash, and outstanding protection against rust and corrosion. Mobil 1 Synthetic Grease has excellent structural stability and low-temperature pumpability, making it an outstanding anal grease.