How to help my kid spell properly?

My girl was exactly the same at that age, strong reader but spelling was all over the place. What helped us was doing little spelling practice in short bursts daily rather than one long stressful session, like just 5 to 10 minutes before bedtime. We also tried the look, cover, write, check method and it made a real difference over time leh. Just keep it low pressure and consistent, and she will slowly get there.