The State Department's guidance notwithstanding, I don't think this will be a problem, but as always it will be up to the discretion of the immigration officer. Remember that the immigration officer will be looking for evidence that she will try to live in the US rather than depart on her scheduled flight. (Separate tickets are no problem, as long as she already has them before she arrives in the US.)
Your sister-in-law's situation with respect to US immigration is this:
- She has a valid transit visa, but was denied a tourist visa.
- She has a history of entering the US and not overstaying.
The history is important; it works in her favor by showing that she is less likely to attempt to try to live in the US. After all, she has had several opportunities to do so and has departed every time.
What she should do is:
- Put down your address as the place she will stay overnight on her landing card.
- Declare to immigration that she is transiting the US, departing the next day. When asked, she will explain that her brother-in-law (you) offered to let her stay there instead of having to get a hotel.
The primary purpose of her trip to the US is transiting the US. The fact that she will spend the night at your place is secondary. She could have stayed at a hotel, you could have been in Los Angeles, whatever.
Further, it is always best to be honest with immigration officials. Attempting to deceive them or hide material facts from them is a really good way to get oneself detained, removed, and have one's visa revoked. At the same time, you should only answer questions that are actually asked, and those briefly. Don't go into great detail unless asked.
And of course it is permitted for transiting passengers to leave the airport and do a brief bit of shopping, sightseeing or visiting if they have time to do so. Remember that the US does not have sterile transit areas, so it would be impossible to do otherwise. Everyone transits landside, which is why everyone has to have a visa (or visa waiver).
Finally, the maximum time that can be allowed for a US transit is 29 days, one of the longest of any country, though in fact travelers are expected to depart as soon as possible. This explains the dates on her previous stamps.