According to:
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-Tourist-Visa.html
Your friend will need:
"Passport or travel document with validity not less than 6 months
Visa application form completely filled out;
Recent( 4 x 6 cm.) photograph of the applicant;
Evidence of travel in and out of Thailand (e.g. Air ticket receipt paid in full);
Evidence of adequate finance (850 USD per person and 1250 USD per family) for the entire duration of stay in Thailand;
Consular officers reserve the right to request additional documents as deemed necessary."
Your friend may be asked to show 20K THB (or equivalent) in cash on entry as well
However, what is your friend's visa history? They are starting to get strict in the embassies