I did our translating from Thai to English as part of the process to adopt our niece. To ensure that everything we did would be acceptable we contacted the court first and asked which interpreters they use and then we used them. We live near Glasgow and the company used was called Global Language Services. Sometimes we handed documents in directly (cheaper and faster) other times we emailed copies of the original and that worked too.
One point which may or may not be a problem for your friend. When we were contacting our local amphur they stated that no woman can take a foreign name unless it's their husband's name. We sidestepped the problem by our (now) adopted daughter having one name in Thailand and one in the UK (the rest of the world actually). Like you say, this may not mean a lot as it is in Thailand.