Is one entry visa enough for Thailand, first flight-cross over then staying afterwards?

My Girlfriend (Bulgarian) is going on a work vacation trip to India, Vietnam and Thailand.
The path she is taking is:
UK > India > Thailand (1 hour flight crossover, in same airport) > Vietnam > Thailand (staying for 5 days) > UK
She has applied for a tourist visa for Thailand. This only works as a single entry however. As you can see, she is technically landing in Thailand for a crossover flight. She then returns to Thailand after Vietnam to complete the work trip
My question is, will her 1 hour stay in Thailand "Use up" her one entry for Thailand visa - Thus making her apply for a new one within a week in a different country? Or will the immigration officers allow the Visa to be used the 2nd time, as she technically didn't enter the country?
Note - she does not have £5,000 in her bank account to apply for a multiple entry visa.
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