I would not rent to this person. A

What do you say to that person as the reason not to rent to them?  

Person A contributes $30K to downpaymentPerson B contributes $40K to downpaymentPerson C takes on a mortgage for $210KAn llc is created and each person has 1/3 ownership.

It is generally illegal to refuse an applicant due to a property's no-pet policy if they have a service animal, but is it permissible in Colorado to charge that person a standard pet deposit?

The police will not want either one of you getting into a confrontation or talking with this person as that can escalate things.

She's no pushover, but she is just a genuinely nice person, as well as efficient.

I have found local government types are worse than the feds or state because in the give a person a little power category.

I think it goes without saying you cannot discriminate against a disabled person as well. 

Person A and Couple B would call me instead of addressing the noise and neighbor issues.  

Personally, I'd incur a vacancy and give the person a termination notice if your rental agreement or lease allows for such (providing it keeps with local housing regulation compliance).