Being from the country of your wife, This is the wife posting btw, She was raised in a very religious nation. That takes time to overcome. Bear in mind that the province or city she comes from has its own unique beliefs and customs when it comes to marriage and relationships.
How long have you been together? When you talk to her, let her know that you love her very much and this activity you are going into won't change that a bit, in fact it may even deepen it. We Filipina women like to give whatever we can to our husbands as long as everything is explained in a very loving (malambing) manner.
Just a word of caution though, Hope you can handle the tigress she would become if she is agreeable to swinging. :-)