This poem is telling us about the low status of women in the patriarchal society. I think the theme of this poem is similar to the short story "The Yellow Wallpaper".
The second line of the first stanza said "Bright top denizens of a world of green." I think "bright top denizens are the tigers. They are so beautiful and the colour of their fur is as bright as topaz. "A world of green" refers to the natural world that is full of freedom. The embroidery Aunt Jennifer had made must be very well because it could showed the tigers prance "proud and unafraid", self-confident. She wanted to be the tigers whom do not fear "the men beneath the tree."
In the second stanza, we are told that Aunt Jennifer's husband repressed her. I think the "wedding band" is refers to the wedding ring on her hand. It was so heavy that she felt like chained by the marriage.
The speaker is seemed like a bit pessimism because of the first two lines in the third stanza, the speaker said "When Aunt Jennifer is dead, her terrified hands will lie still ringed with ordeals she was mastered by." She thinks Aunt Jennifer couldn't relief even after her death. Her "terrified hands" will still suffer from the oppression of her husband. She didn't has any freedom and she was totally controlled by her husband. She had no rights to talk about her feelings in that period. It was impossible for her to change the system. The only way she could do to express her feelings is by needlecrafts. This is very common for the women to learn it at that period.
The embroidery she made showed her desire to protest against the unfair status of women in the society. She hoped women would have higher social status just like the tigers "prancing, proud and unafraid"