In Shrek The Third, she is first seen during Fiona's baby shower until Prince Charming invades the castle and the princesses and Queen Lillian escape secretly. Eventually, Rapunzel pretends to find an exit and runs all the way to where Charming really is. The princesses and the Queen follow but are cornered by Charming's knights. Rapunzel then shows off her love and affection towards the Prince and the ladies are imprisoned in a dungeon. While they are imprisoned, Rapunzel is practising for her role in Prince Charming's play. In the final performance, she sings and acts as a princess on top of a tower (mimicking Princess Fiona, whose situation itself was a mimick of Rapunzel's) but the play was interrupted by all of Shrek's friends and wife. Gingy enters the stage by holding on to her hair as he quickly gets down. He accidentally pulls all of her hair and Rapunzel gasps in horror (when it is revealed that she is actually bald). She later runs away from the stage due to the embarrassment it is unknown what happens to her at the end of the movie.
Unlike the rest of the princesses, she betrayed the group by siding with Prince Charming and assists in his evil plans. It is revealed in the end of the movie that she is actually bald and she's wearing a long braided wig. While unlikely, this could be a reference to the fairy tale when the witch cuts off her hair. It should be noted that she actually has a sympathetic side. This is evidenced when she reminds Charming to not hurt Fiona and the princesses and Queen Lillian as he promised. Also, as they are led to their dungeon, she turns back and gave a sorrowful expression on her face. She is snobby, opinionated, vain, and doesn't seem to get along with the bossy Snow White in particular.
Prince Charming - it is shown that Charming is Rapunzel's boyfriend. They both seem to be in love with each other when they are seen kissing.