It's too late to make your wife an employee for 2017, unless you want to pay a lot of fines, penalties, interest and late fees for not having filed and paid the required quarterly withholdings payments for the employer side. As a sole proprietor or single member LLC, all income is reported on SCH C. Period. But there's no reason you can't hire her now for 2018. Keep meticulous records and make "SURE" you file the required forms each quarter (each month if your state requires it) and pay the employer side of her SS and Medicare tax. The fines for a business for not doing so, or for paying late, can be rather high.
Remember, if your state taxes personal income, then you have to deal with that too, in addition to the IRS.
