I am an authorized and trained leader on Precepts, and would say no and yes. A Calvinist? Yes, like Charles Spurgeon was a Calvinist, yet a Baptist.
Reformed? As in Reformed Presbyterian? (no) Or Reformed Baptist? (yes).
These are my impressions and in no way an official response.
The beauty of P on P is the answers are not dictated, but through deep inductive study each participant is asked to come up with their own understanding of what scripture says. This is by far what we all should do - before ever going to commentaries or the opinions of others.
Many of the problems in Christendom come from believers NOT knowing scripture themselves - everything they believe comes 2nd hand, from a preacher, teacher, Sunday School, or a book. Christians are spiritually weak in general because of this: they do not have a first-hand knowledge of scripture. What they have is pre-digested food from others. It’s like living on Gerber’s Baby Food as an adult.
Kay’s methodology is rock solid in a methodology for studying scripture, and her works do not push a particular doctrine. She should be commended for what she has done. Sad that no man did what she did. When men fail to lead here, God will often raise up a woman to do what a man should have done.
Jesus was a teacher. There is nothing inherently wrong with learning from a teacher.
The Holy Bible is a book. Likewise there is nothing inherently wrong with learning from a book.