Okay, I’ve been down this road. For the Holly Barker series, you want publication order. It’s a straightforward one because the series basically just is a linear progression of her life from police chief to troubleshooter. The first one is 'Blood Orchid', where she's introduced as the police chief of Orchid Beach, Florida, dealing with a murder right after she’s moved there.
From there, you go to 'Iron Orchid', then 'Shamrock Green', and 'Bloodstone'. The final book is 'Bone Valley', which came out a few years ago and kind of feels like a late-stage encore. Honestly, reading them out of order would be confusing mostly because the supporting cast and her relationship with her dad evolve in real time. They’re not super complex thrillers, but the continuity matters.
I’d skip the weird omnibus editions that mix series; just stick to the core five in the order they were written. The later ones, especially 'Bone Valley', have a different, slightly slower pacing that might feel off if you haven't seen her career build up.