... what kat said
I usually just handwash with a teensy bit of baby bath before lanolising (too scared to felt them in the machine!)
You could also just ask your friend if she minds if you wash/don't wash them. Or how she likes them washed.
Because for me, I would wash & prelanolise for a friend to try out for the night, then wash after the wollies are returned.
All the best!