and she looked smiling at all the other members of the company. Yes, we understand, we understand, she thought[...]

The thing is that Miss Brill has taken this habit too much to heart. She sees the people in the park as actors in a huge play. She sees herself as part of the scenery, and this is what makes her so emotional about the whole thing: she finally gets to be a part of the world, in her terms.

So strong is her attachment to the fantasy, that she does not ever realize how strange she looks like in the eyes of the world, or how odd the whole thing is. We are never told, as readers, whether Miss Brill even acknowledges herself as it is; whether she recognizes her awkwardness. So detached is she, that she even "hears something crying" when she has to rush home after hearing the young couple laugh at her and her "old smug". Especially, when they laughed at her beloved fur. 

Therefore, the Sunday trips are mental escapades for Miss Brill. In them, she gets to be whoever she wants, and feel freely accepted by the rest of the world around her. We are hinted that she is, perhaps, taking this habit too seriously, and becoming too attached to it. The crying at the end shows us that her fantasy has finally cost her a fragment of her pride and dignity, after all.

Miss Brill enjoys—or convinces herself she enjoys—her Sunday afternoons at the the Jardins Publiques. She can dress up for this outing, sit in what she calls her "special" seat on a park bench, and listen to the conversation of the people sitting next to her. She can also people watch, as couples and groups and children go by. The park outing is a chance to be outside and not sitting all alone in her small rented room.

As she watches the people on her bench this day, she decides that by coming every week, she is alike an actress taking part in a play. She thinks to herself:

How she loved sitting here, watching it all! It was like a play. It was exactly like a play.

Actually, she is a poor, lonely old woman who works as tutor and companion during the week and has nothing else to do on her Sundays off. The park is free, and as she walks home, she usually buys herself the "treat" of a slice of cake. She is like other old people she sees at the park, who come week after week. She calls them "funny," but realizes by the end of the story she is one of them. We could admire Miss Brill for bravely trying to make the best of her life.

Miss Brill, a British expatriate who teaches English in France, leads quite a lonesome life in her adopted country. From what the reader learns,  Miss Brill has made a habit of going to the public gardens on Sundays to watch people. 

While she is there, she uses her imagination to give character traits to everyone that she sees there. She compares this experience to going to the theater; she makes up stories using the people whom she sees, pretends to know them, and engages in an active, imaginary storytelling with herself. 

How she enjoyed it! How she loved sitting here, watching it all! It was like a play. It was exactly like a play. Who could believe the sky at the back wasn't painted? [...]They were all on stage. [...]they were acting. Even she had a part and came every Sunday.

As you can see, Miss Brill's only connection with the mainstream of society is through her imagination. She has made small connections through her job as a teacher, as a reader, and maybe even at her boarding house. However, the big society that looms in the horizon is way too big for someone who is obviously so little prepared to deal with the real world. 

Therefore, the main reason why Miss Brill goes to the public gardens is, first of all, out of habit; she has made it her sole and most significant form of entertainment. Second, because she gets to enter the "real world" through a fantasy. Third, because it soothes what is definitely a terrible loneliness.

She feels happy and part of something real. It is, perhaps, a safe way to be "alone, together". For some people this may seem awkward. However, there are many people just like Miss Brill who fear the sacrifices and risks that come with making human connections. 

Miss Brill lives in a very small room and has very little money, so she finds it exciting to get out into the sunshine and fresh air and to see other people at the park, even if she doesn't know them. She enjoys getting dressed up for her outing to the Jardins Publiques, such as by putting on her fox collar, and she likes listening to the band that plays in the park. It is a pleasure for her to watch the people passing by and see the children playing. She also likes to listen to the conversations people sitting near her have.

She finds exciting, too, the sense she has of being a character in a play that is performed every Sunday. She likes the idea that she is not just part of an audience watching what is going on, but a participant in a recurring drama.

However, there are hints all along that Miss Brill is working very hard to repress the fact that she is sad, poor, and lonely. She stops herself and changes her internal narrative every time the word sad comes rising up to her mind. For example, when the band begins to play again after a break, she starts to think there is something sad in the music, but then says to herself, "no, not sadness." Yet eventually, reality will intrude on Miss Brill's fantasy.