Aunt (or cousin) Dete has been worried about what has become of Heidi, Peter, and the goats. She looks all around for them. She climbs to the highest point she can find to try to see them. She doesn't realize that Peter knows places off the beaten track where the goats can graze on good food and so has gone there with Heidi.
When the children finally return to the hut, Aunt Dete begins to question Heidi sharply, because she has shed most of her nice clothes and appears only in her short-sleeved underdress. Heidi has done this because she was hot and uncomfortable climbing around the mountain in her heavy cape, shoes, socks, and Sunday dress. Dete, however, is upset about what has happened to these good clothes, and she questions Heidi about where they are. Heidi points them out in pile of clothes down a slope, and Dete pays Peter to go get them.
This scene shows that Aunt Dete does not yet fully understand the extent of Heidi's free and natural spirit. It is probable, too, that Dete, who is a good person at heart, overreacts because she has been worried that something had happened to Heidi and Peter after they disappeared.