Just a few points with my 2 cents worth thrown in.
Many times when she needs help with house or yard she will call me.
1.I assume you must have your employees give her the help she needs?
2.Has she paid for this, or do you provide it quid pro quo for all the business she sends you?
3. How do you know the neighbor isn't a drunk with an ax to grind with the vet and willing to trash her reputation?
4. Seems unlikely that a sloppy drunk could keep a viable veterinary practice in operation...but that could be debatable I suppose.
She told my nephew he could pick up check tonight between 5 -6 pm.
1. Could be an honest mistake, emergency came up perhaps, or she went out for the evening and simply forgot.
3. If the above is true than my opinion is that it's best to give someone the benefit of the doubt before you get trigger happy and start off with threats.
4. Some people are more casual than they should be with payment for services rendered. It's not right, but it's a fact of doing business.
....................................A personal anecdote:
I gardened for a well known and very wealthy native son for several years. I bill all of my clients monthly. He always paid, but was always 3 weeks after receiving my bill.
I put up with it because I knew he was good for it, maybe I should have kicked up a little dust over it, but I never did.
When it came time for me to make some decisions about how many clients I could actually maintain without working myself to death he was the first one dropped. He wasn't too happy about it but I let him know that the inconvenience of delayed payment factored in.
I hope your nephew gets paid tomorrow and this doesn't turn into a bad situation.