To be on the safe side, your wages should represent fair market value for the services you actually perform for the business. They should be similar to the market wage the business owner would have to pay to hire a stranger with similar skills to perform similar work.
For example, if this is a landscaping company and landscapers in your area are typically paid $20/hour, it would probably raise questions if she paid you $40/hour. On the other hand, you may be currently underpaid because of the financial situation, and a raise would bring you in line with the market (at least on paper).
However, aside from the tax situations, I worry about your mortgage lender. In reality, you are buying a home together. You are suggesting that you buy the home by yourself, and you show the mortgage lender a W-2 from ABC, LLC showing that you make (let's say) $100,000 per year. You don't tell the lender that ABC, LLC is owned by your romantic partner and shows a $100,000 loss on its tax returns. If you did tell the lender all these facts, the lender would realize that the actual money available to the household to pay the mortgage is much less than what it appears on paper. This is also why a fair market wage may be important. If your partner goes out of business, you should be able to find another job performing the same tasks for a different business, at the market rate. If you are being paid an inflated rate, your "income" would drop and the mortgage would be at risk, but if you were being paid a market rate, your salary wouldn't change, just your boss. Of course, I don't know all the facts, but I would be cautious about this arrangement.
