A lot of misinformation here. Just a quick search on the US cdc (https://www.cdc.gov/coronaviru…tizens-US-air-travel.html) will show she should be eligible to travel there unless she used an unacceptable vaccine.
Also for traveling what matters is the location the individual was within the last 14 days to a month, therefore her Thai citizenship shouldn't affect her since she has been in South Korea/France. Although I'm not certain but I also don't think she'll need to quarantine (if Jennie and Rosé didn't need to) if she's fully vaccinated and has a negative pcr test since she has been in SoKor for the last 14 days.
Now there might be other reasons of her not traveling to the US that are unknown to us but that's left to YG and her. Anyway, I think it's best to wait before making assumptions on the reason she may not be attending if true. I doubt any official statement has been put out on her being unavailable for the event and also her upcoming schedule isn't known yet.