The Daughter is attracted by the Light in Obi-Wan and decides to give him her blessing, which comes in form of sex, naturally. Obi-Wan is a bit perplexed, but goes along with the ride, because, well, it is not really happening anyway and the Force literally wills it, right? And we all remember the appraising look he gave her when she appeared.
The sex, however, comes with a lot of praise from the Daughter who feels that Obi-Wan is basically her champion and Obi-Wan does not really know how to deal with this shower of praise.
Whether their height difference is apparent or the Daughter scales herself down to match Obi-Wan is up to the writer!anon.

Crack possibilities to explore: the Daughter's blessing grants Obi-Wan's cock the ability to pull people back to the Light side.