Also a reminder: if you modify your reservation (change dates), you lose all the 'cancel any time' and 'refundable before this date', features. When you submit your date change they charge you in full and it is non-refundable at that point.
Since you said 80 days is the intention, the wisest course would be to apply for TR60 at a consulate in Europe. On arrival to Thailand she will get 60 days stamp. This stamp can be extended for additional 30 days without exiting Thailand. (1900THB at local immigration office).
2) If your flight leaves from Don Mueang Airport, take the SRT Red Line to Don Mueang. DONE.
3) If your flight leaves from Suvarnabhumi Airport, take the MRT to Petchaburi station. Go upstairs to Airport Rail Link(Makkasan)...then take that to the airport. DONE.
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