I’ve done it 5 times over the last 8 years and all 5 were successful. As long as you can prove that you can support her for the duration of the trip and that she has something to go back to then there should be no problem.
My girlfriend stayed in a UK hospital for a week last Christmas with a kidney infection. The bill came to thousands but luckily she took out insurance with a Thai company before she came and they were very efficient and covered everything.