Licia is a con-artist and possibly a murderer. She may not even be a 'real' cleric, and may have stolen her gear and miracles from someone else. She sells items and miracles, most likely just to make some souls.
Licia hails from the land of Lindelt, a place that is governed by stringent commandments and a religious sect. She has studied the art of miracles and become very adept. It is a common Lindelt practice to send trainees on a journey into other lands for ascetic training, however it is implied that Licia may not have come to Drangleic of her own volition.
Prior to Licia leaving for Drangleic, a pair of ancient and powerful miracles called Bountiful Sunlight and Soothing Sunlight were stolen from the Lindelt Monastery. When first meeting her at Heide’s Tower of Flame, Licia explains that she thought the place would be bustling. She then goes on to attempt to sell you miracles. When she tells the Player she will be moving on, she lets slip that she came to Drangleic to “gull the…” (i.e. fool or deceive someone), but then immediately corrects herself saying she came to “help the gullible by teaching the good word hehe…”.
Licia carries the Idol’s Chime and wears the Saint’s Set. These items appear to be unique to her. The Idol’s Chime indicates that Licia has “unusual urges” that she acts upon out of view of others. The Saint’s set indicates that it is rare for clerics to pass through life without trouble, and that not all clerics are what they seem.
From the above, it seems clear that Licia is hiding something, and it is not too much of a leap to suppose that her goal is to extort the hapless and gullible by selling them miracles, even going so far as to sell miracles she just made up (e.g. Caressing Prayer which is really the sorcery “remedy” from Dark Souls 1). She is likely the one who stole the ancient miracles from Lindelt, and while she keeps Bountiful Sunlight on her person, Soothing Sunlight is only gained when reaching the highest rank of Blue Sentinels covenant. It is likely that she gulled Blue Sentinel Targray into purchasing that miracle off her upon arriving at Heide’s Tower of Flame, and that he was charged such an exorbitant fee, he now considers the miracle to be incredibly precious (as you only gain it under hard-won circumstances).
Licia is also more ruthless than we may at first realise. She wishes for her goals to be unperceived and when the Player finds her out using the Crushed Eye Orb (which seeks out miscreants), she explains that she can now finish you off “guilt free”, implying she has killed before to save her skin.
Finally, Licia may have studied at Lindelt, but she does not appear to have truly engaged with the topics presented there outside of a rudimentary knowledge only utilized to further her gain. She will preach in awe on the origins of miracles and their great value, but then when pressed for further information, will tell the Player they cannot comprehend what she would tell them. From this dialogue it is clearly implied that she does not know anything more.
Despite all her failings, Licia is a powerful miracle user, and while she may be selling you miracles to extort you or prey upon your gullibility, she is also providing you with miracles that actually work and help you. It seems that Licia isn't purely evil, but nor is she good.