I don't know the answer to your specific question. However, here are a few things that might help.

1. If she is in Biz, she will have access.
2. You can log in to her Skymiles account and purchase it with your credit card.
3. I think you ought to be able to purchase a discounted 1 day pass on the "trip extras" section if you can access her "my trips". 2 of them would be less expensive than the 30 day membership.

I'm sure the old pros will be around eventually to give you the correct answer.