What documents does my fiancée need to present at passport control in Germany?

The user is preparing for a flight from Bangkok to Germany with their fiancée and is seeking advice on necessary documents for immigration control in Germany. They are unsure if their comprehensive documentation, including a letter of guarantee, invitation letters, a valid visa, proof of relationship, vaccination records, and PCR test results, is sufficient. Community responses suggest that, primarily, her passport, visa, and possibly the vaccination certificate will be important. Additionally, they caution about the validity of the PCR test and mention the potential need for COVID insurance.