Cutting her off would basically mean the end of the relationship, and I'm not ready to throw in the towel yet.

she has a respectable endowment

So HN, how would you deal with someone that has a bad attitude, lacks pride of ownership and quickly gets defensive? What management strategies would you use to reach this person, get them more invested, and help bring out their passion?

It sounds to me like your little startup is more important to you than her. Also: getting real life relationship advice from strangers over the internet is either a huge miss or hit.

This is why you (try to) keep business/personal separate. Money changes (some) people.