If I understand the OP, daughter needs just a one way ticket. This will be expensive and many full fares allow free stopovers.

Alternatively, it's an airline industry that a stop under 24 hours on an international itinerary is considered a connection (no additional charge, assuming that it's a legal routing for the fare) rather than a stopover.

USA to BKK via Europe, including IST, will probably be more expensive than TPAC routings because the legal routings for Asia east of India tend to be TPAC. To connect in IST or elsewhere in Europe is likely to be equivalent to buying two tickets: something like USA to IST and IST to BKK.

Try to include her local flights exBKK on the same ticket so that luggage can be checked through and she's protected in IROPs.