Can my granddaughter travel on her British passport while her Thai passport is being renewed?

Hello this site has helped me in the past understanding the visa exempt process. Thank you.

However, I now have a different question regarding my granddaughter who holds both British and Thai passport.

My son lives in Thailand on a work visa, he has 50% custody of my granddaughter. Part of the custody agreement allows my son (and us as grandparents) to take our granddaughter out the country on holiday for 2 weeks per year.

We must give 14 days notice, I have given over a month.

The issue is my granddaughters Thai passport needs renewed, my Thai ex daughter- in law is making excuses not to renew it. My son however renewed my granddaughters British passport last month.

We want to take our granddaughter on holiday for 4 days. Will there be any issues if we use her British passport to leave and enter Thailand? I will have the custody document in both Thai and English plus the agreed travel insurance and medical approval.

Thanks in advance for any help.