I’m trying to bring a Russian woman to the US to live with me. We want her to stay with me for 6 months, and then decide if she should apply for a K1

You can certaininly apply for a tourist visa first. That will allow her to stay in the country for 6 months. You can file for a fiance visa while she is in the US. However, there are limitations about time of filing. We recommend waiting 90 days. Additionally, keep in mind that Fiance visa takes a long time to process.  This answer is intended for informational and educational purposes only and should not be considered legal advice nor forming the attorney client relationship. For initial consultation, call at 480-467-3188 or email at admin@cronuslaw.com.

Yes. If she enters the US on a visitor visa, the CBP may ask her questions about her plans. If she says she is visiting her boyfriend that's ok, but if they sense that she is concealing her intent and that she really wants to get married and stay permanently then that could raise red flags. It's ok to intend to visit and then after arrival change her mind and want to adjust status. But concealing one's intent is immigration fraud. You should have a free consultation with an immigration attorney to discuss.