Want to live in the US for 3-6 months

My business partner, a Canadian citizen, wants to move down to the United States and live there for about 3 to 6 months. She does not want to work in the US. Now, the money we make as a business would not be sufficient to support her stay, so basically she would use her savings to support herself.

My questions are - is she allowed to do this? What does she need to do/show to American authorities? What implications are there for our business, which is operated in Canada?

She needs to show that (a) she will maintain Cdn residnence throughout her stay (b) has sufficient funds to live off and (c) most importantly, will not engage in any business activities while in US.
Methinks, from what you said, that (c) will be the hardest part to prove, because of (b)

Thank you for this information. When you say any business, does that include ours? Some added details - we run several websites and make our revenues from advertising. Most of our advertising comes from America companies like Google and Amazon. Furthermore, we occasionally undertake trips into the US, for business purposes. But for the most part, the websites we run can be run from anywhere in the world.

Also, is their some kind of dollar amount that the American authorities would have in mind (say $10 000) that she would need to have, on which she could support herself while in the US?

There is a difference between business travel, and wanting to live in US doing business. That you cannot do.

for other questions, why not ask at the border, since they will be the ones deciding.