I'm planning on bringing my Indonesian girlfriend to Thailand with me next week for about 3 weeks. We'll be flying in from Singapore. Should we expect any hassles from immigration? Will she need a R/T ticket?

I think if it is really only for 3 week, she does not need to apply for a tourist visa. She can get an "on arrival visa" valid for 1 month. If your gf can get to Sg (not on transit) without any hassle, she will have less hassle in TH. Sg has stricter tourist laws for Indons.

http://www.mfa.go.th/web/12.php#Tourist

TOURIST VISA EXEMPTION

-  According to the Interior Ministerial Announcements dated 1 October B.E. 2545 (2002), 20 December B.E. 2545 (2002) ,18 October B.E. 2547 (2004) and 6 May B.E. 2548 (2005)  , passport holders from 40 countries and Hong Kong SAR do not require a visa when entering Thailand for tourism purposes if their stay in the Kingdom does not exceed 30 days.

Indonesia is in the list.

TEMPORARY TOURIST VISA : VISA ON ARRIVAL

        -  According to the Interior Ministerial Announcements, passport holders from 20 countries may apply for visas at the immigration checkpoints for the purpose of tourism for the period of not exceeding 15 days.

        - The applicant must possess  means of living expenses 10,000 Baht per person and 20,000 Baht per family accordingly.

        - The applicant must produce full paid ticket which is usable within 15 days since the date of entry.

        - Visa on arrival is provided at 23 designated international checkpoints and applicants should produce the application form to which his/her recent photograph (2 ½ inches)  is attached. The application fee is 1,000 Baht.

        - Visitors who enter the Kingdom with Visa on Arrival generally cannot file an application for extension of stay except in special cases such as illness which prevents them from travelling, etc. They can submit an application at the Office of Immigration Bureau , Immigration Division 1, Soi Suan Plu, South Sathorn Road, Bangkok 10120. Tel. (662) 287-3127 or 287-3101-10 ext. 2264-5 or at website http://www.police.go.th/frconten.htm

However, they make ask for a return ticket if they suspect she is staying longer than the 1 month.

I think you should get a return ticket too......just in case. Get one where you can change the return date easily. It may be more expensive but better safe than sorry.

Good luck

Thanks!