Can you define how your GF was hassled? What have been her travel patterns to/from THL?

Carrying an Indonesian passport means she gets a 30-day Tourist Visa Exemption.

She is trying to satisfy the 90-day bounce required by a Vietnam visa?

Maybe fly to PNH, or BKK (rather than DMK)?

I don't think she will be able to turn at DMK, back to HAN, without passing arriving Immigration, checking in, passing departing Immigration and security. Same-same if flying onto CNX.

Clearly there's more detail, and I understand not wanting to share it, but I really think she should look at alternatives. Fly down to SGN and do a land exit/entry at Moc Bai?