+2 everyone's comments
Most people will try to jump through a bunch of hoops to keep their properties in Sch E instead of C (ex: renting an airbnb property for a several month lease in the off season). If you want to establish the LLC and property management business going forward for liability reasons, that's fine but you need to separate your finances to avoid piercing the veil. Since you mentioned you didn't do that for 2018, there's no reason to try and take the SE tax hit of Sch C.
If your SO does not work a FT job and you all think she works enough qualifying hours, then I would start logging all time spent on the rentals with a note of what each time block is for with the idea that you all may need to justify the real estate professional designation to the IRS. I'm not a tax professional but from what I've read on the subject, I do think four properties with a real estate professional designation would be an audit risk.