it doesnt matter which number she will see first. The most important is just pick gate number and wait there. Or like I said wait at the "meeting point" sign. So they wont miss either way
Arrivals is on 2nd floor. After she pass the immigration, she will collect luggage, then customs, then she will come out. When she comes out, she will trun right thats everyone heading to. Tell her to look at her left side where she can see the gate numbers 1,2,3 etc. You pick the gate number (for example 5), wait there and tell her to look around (from your direction, those numbers will be on your right side). Or you can also tell her there is a sign "meeting point" where everyones waiting and your able to see whos coming out. You cant go further than that point.
I assume you want to apply for a tourist visa. (1) Check Thai embassy Hanoi website link visa category page and pay attention to the number 7. (2) Write an email to the embassy to clarify if Indian passport holders are eligible to apply for Thai visa outside India as it said certain nationalities are required to apply from home country. (3) If your on tourist visa for Vietnam, make sure its valid before you apply for another country visa. (4) Once the embassy confirms Indian passport holders can apply for Thai visa outside India, just go there and submit all the documents shown on the link. Hope it helps.