B1/B2 Visa Entry to the USA question?

A return ticket is one factor in being admitted. Honestly, it's not the single most important factor. Having a visa counts for a lot because someone in Thailand looked at her and decided that she has sufficient ties to Thailand that she'll return. Having sufficient funds for her stated reason will help. Having been to the US and returned will help. Having a return ticket will help. Having an acceptable reason for her visit will help. (But this is the easiest part of the admission interview. Everyone wants to see the sights, visit big cities, see Mickey Mouse.)

If possible, she should get her return ticket before she leaves. This helps everyone. If she's confident that she'll stay a month, get a ticket for that return date. If she's not sure, "maybe two months, a bit more," She should get a ticket with an open return date. She'll need it to avoid problems. Visiting costs money and if she runs out of money before her flight back, she'll be better off with an open ticket, so she can schedule her flight and leave a bit sooner than she thought. This will be easier on her than running out of money and having nowhere to go until her flight leaves.

Bottom line- you are partially right, a return ticket helps. But it's not absolutely necessary to be admitted, though her reasons to return and her resources to stay could become greater factors in the admission process. ... Take care!!

they should have a return ticket ,... you purchase the ticket long before you get to the airport