51 views and no reply just means none of us has been through this before ourselves.
The house you own is both a long term investment, and it is a business. You have to split things in terms of buying the Capital Asset, paying Capital Repairs and paying Expenses.
As an investment, you have borrowed money to invest, and you are gradually paying off the loan. Rental income that is paying off the mortgage is reducing your debt, therefore it is money in your pocket, therefore it should be considered income. Paying the mortgage isn't an expense, it is the actual investement. This is your Capital Asset.
From a business point of view, what you spend on repairs should be an expense. Capital repairs are maintaining and increasing your investment, if you don't repair you lose money. Any renovations will probably improve your investment. If the house were vacant you would still have to repair the roof or you would lose thousands of dollars of value. This is a grey area that your ex could challenge if she wanted to but you are probably safe deducting this.
Utilities, I presume you pay and then rent the property with utilities included. This is an expense. If the property were idle the utilities would be negligable. Other expenses would be costs to rent it out, like advertising, and time spent managing the property which would include collecting rent, inspecting damage, hiring contractors and accounting and banking. You would have to show that this time actually cost you, for example if it had to be done during business hours and you took time off work to do it. Otherwise, the cost of hiring a property manager would be the equivalent.
So I would say the safest way would be to deduct everything but the mortgage payments and then you look like you are doing your best to be fair and honest.