Maybe a partnership might be better? One of our businesses is a partnership (we both have sole trader bus as well )between hubby and I and at the end of the year Tim the wonder accountant assigns profits where they are most beneficial.
If the cake bus was in your name only you would have to pay wife award wages, super, work cover etc etc etc. a partnership between you and her circumvents this. Check with your accountant before registering for the ABN