Are you under 'old rules' or 'new rules' ?
Old rules are visa applications submitted before 9th July 2012
If she's under old rules then it's ILR after the qualifying period of 24 months living in UK
If it's under new rules I personally don't see any problems from the situation you describe.
The incomes can be combined provided they relate to the same financial period being used.
Here's what UKVI state in the
Annex FM Section FM 1.7: Financial Requirement
Look specifically under 9.3.6
If you have a good accountant he'll be able to help prepare your documentations
Robbie, is this a sole trader/partnership business or a limited company?
Additionally, have you checked you local immigration office to understand any differences etc between your rules and that of UK immigration rules ?