YA Fantasy where a girl learns she has powers. There is a young man who she sees watching her, and he is dressed in old fashioned clothing.

[Kaylin]

I read this book around 2014. It is definitely part of a series. There is a girl in high school who keeps seeing a young man dressed in older clothing. She eventually finds out she has powers. A huge part of the plot is that the young man is a lover from a previous life, and he also has these powers. Basically, when these people with powers die, they are reborn in a different life. The bad guys are there to find them as they are reborn and kill them again. After a certain number of time they are killed, they die permanently (I think). I remember a part where there is a big fight at her house. I also remember her being captured and put into a small, confining area where she isn't able to use her powers.

[Florence]

This sounds very like Book of shadows by cate tiernan, first of the Wicca series (published as the sweep series in some places). Morgan discovers she is a blood witch, and she was adopted. Near the end of the book she is imprisoned in a small room.

[Kaylin]

Just checked, it isn't that series. I don't believe she was a witch. More so just had powers. It's similar to the Wings series by Apprilynne Pike

[Charlotte]

The Eternal Ones by Kirsten Miller?