I read some of the series, not all of it, around ten years ago, though they were likely to be older. I think the series had at least four books. The story follows two time lines, one "current" and the other in the past. The time line for the past is the majority of the story, while the "current" time is where the primary female character (and possibly a very limited few other minor characters) are from.
The main female character, a young adult of late 20's ot early 30's, visits somewhere in the UK. In or near Scotland, I think. The visit was probably to research her family history. I believe this search was prompted by the death of someone in the family, but not sure. She is set to meet an information source in the countryside, and somehow ends up crossing a "magic line" or entering a "magic circle" that shifts her into the past. She arrives at a time of conflict in the area, though I don't recall what it was about. I do remember that she ends up falling in love with a man from that time who is also on the loosing side of the conflict.
In the first book she manages to "diagnose" the medical problems of a nobleman, Lord or higher, that is a prostrate issue. In some fashion she ends up "connected" to the family, or clan, on one side of the conflict and the successful diagnosis, and eventual treatment of the medical condition secures the freedom, or life, of her beloved.
At some point in the first book she returns to the current time and investigates some of what she "remembers" from the past. She's not sure she really experienced it, rather than dreamt it. In the current time she also has an extended conversation with a religious figure (priest. parson, or some other local clerical person) and I think she learns some of her past, that's not good, and reveals some of what she's done recently. There may also be a pregnancy, possibly from a rape in the past time-frame, that is dealt with in the current time-frame.
In the other book I read, probably the fourth in the series, the "past" has progressed to the time where Kentucky, USA, has been claimed by the Europeans, and I don't believe the American Revolution has happened, or at least isn't final, yet. On the other hand, it's possible that that war has ended and Kentucky was a county of the Commonwealth of Virginia. In either case, the laws of Kentucky were still from an outside source, and I think the making of Bourbon was not allowed then, or the main characters were not permitted to make it anyway. The male and female leads are the same people, aged naturally, as the opening book. So, the series cannot cover too much time.
In the non-first book that I read it is discussed that the ability to return to the "now" still exists for the female lead, and that it is accomplished with the use of some special gems. These gems are hidden inside an hour candle. I think there were five gems, and that to avoid some problem arising in the book a retreat to "now" was an option. One problem with that option was the need to "save" more of the family than five gems would accommodate. There is also a scene where the female lead, from our time, is trying to create penicillin. Somehow she knows enough about penicillin to distinguish that variety of mold from others, but is not 100% on the process to create it, so she's growing many cultures and examining each by microscope looking for the right one.