Many national private and hard money lenders do not lock rates until the appraisal is completed and approved because the numbers that come back on the appraisal really impact the pricing, if the market rent/values are off.

Typically I would just run it through my name but there are areas of ohio that target out of state owners if its a single family and will send you fines and violations  for every little thing. you also should talk to your attorney and accountant on how it impacts taxes

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If you co-sign, the loan will consider both your incomes but also both credit scores, so her credit could impact the terms or buying power.

Also make sure you understand everything about adding an ADU including value of the ADYPU, financing, impact from rent control, duration between initial expense and initial income, true cash flow (know the 50% rule, at 50% rent ratio initial property tax will be near 20% of income)- educate.  

Some are actually more environmentally friendly, more stable and more secure.

These people are a pain in the arse, get a good Environmental company to do your Phase 1 and any permitting you might have to do for stream crossings, wetland compensation, ect.

However, the loan could still impact her indirectly.

Assuming the insurance premiums don’t significantly impact my cash flow (which is one of my primary goals), how do you assess the risk of taking out a loan under my personal name versus opting for a commercial loan that requires a larger down payment and comes with a higher interest rate?

This is where a sale may benefit you long-term if you can find an investor to take it before the increased rate and pending rent decreases impact the value of the property further.