If her English is not fluent, why is she giving interviews in English? Speak in Thai to reduce the chances of misunderstandings.
She is trying to connect to her English audience obv she will try with English. Even though she is not fully fluent and may not get everything across but she will surely improve...
Twitter hate shouldn't be the reason why she should communicate only in native language.. if that was the case she would never learn and improve her Korean but look at her, she is so proficient in Korean now even to the level of locals praising her...
As she said" Maybe in two years, I will be a local" in English.