Technically, laquelle and qui might be used in either or both case in your sentence.
Grâce à toi, je suis avec une femme à qui je me dévoue entièrement, à laquelle j'ai donné mon cœur.
However, one slight difference is laquelle usually means "one from a known set" while qui has not this restriction and is then open.
See the difference between:
– À qui vas-tu offrir ces fleurs ? → The question is open, anyone might receive them, including more than one person or just nobody.
– À laquelle vas-tu offrir ces fleurs ? → It is assumed by both parties that a list of potential receivers is known and one and only one of them will get the flowers.
This explains why the first sentence is the one that would probably be the most natural. Moreover, French tend to avoid repetition so your second suggestion would be also less likely to be used.
When following a preposition like à, pour, vers, de, avec, sans, etc., the pronoun qui is restricted to living beings, whatever their gender or number.
On the other hand, laquelle refer to singular and feminine word which can be a living being (qui), a thing (quoi) or a location (où).
‑ À qui est cette voiture ? (Whose car is this ?)
‑ À laquelle (d'entre vous) est cette voiture ? (if said in front of a group composed of men and women, the question is not directed to the men)
‑ À quoi j'ai droit ? (What am I entitled to ?)
‑ À laquelle/Auquel ai-je droit ? (Which one of these am I entitled to ?)
‑ Où tu descends ? ( Where will you get off ?)
‑ À laquelle tu descends ? (At which one (of the stops/stations) will you get off ?)