This feels a bit overcomplicated. Like the protagonist gets killed by a serial killer, which feels so unusual and traumatic that it ought to be a major plot point, but then it's not, so maybe their death needs to be more mundane, or more relevant to the life they lead in the new world. If they died to a disease it'd make their new life in a strong, healthy body feel like a "fresh start", or if they were murdered by their lover then being a bodyguard to somebody possibly being targeted by a suitor would feel thematically appropriate. Or if the serial killer angle is the one you take, there needs to be some kind of parallel narrative where she keeps seeing or being able to influence the world she's from and she's desperate to stop the killer on the loose, like that should be the core conflict; her duty in her new world versus her unfinished business in the last.
Not gonna lie, as a lesbian I read the opening of "lady gets isekai'd into a scenario where she's the bodyguard to a princess" and was like "oh hell yeah!" because I thought the princess would be the love interest, and was then disappointed that the actual love interest is a dude who's somebody else's bodyguard! That said, a romance between a rival bodyguard could be interesting, like a "friends to lovers" narrative.
There are lots of cool elements here, but you need to try to pull them together with some kind of cohesive theme.