If you go along with the idea that the song 12 Days of Christmas was once used as an aid for basic Christian instruction, then the '9 ladies dancing' may represent the 9 attributes of Christian living that are the fruit of the Holy Spirit.
The 9 virtues, or aspects of the 'fruit of the Spirit' are listed by St Paul in his letter to the Galatians like this:
"...the fruit of the Spirit is love, joy, peace, patience, kindness, generosity, faithfulness, gentleness, and self-control. There is no law against such things." Galatians 5: 22 - 23 (NRSV)
There would be so much more joyful dancing in the world if that sort of fruit was cultivated.
It is the work of the Holy Spirit to produce such fruit in those who 'live by the Spirit', but this does not happen in an automated or magical way. That work also requires our co-operation in encouraging and practising those virtues.
Thankfully 'there is no law against such things'.
Happy 9th Day of Christmas!
Image Credit: Prayltno on Flickr, CC License