Almost everything in this poem is sarcastic unless you are going to take seriously the idea that Bradstreet is really saying that she, like all women, is not competent to write decent poetry. This poem is saying that her work is no good because she is a woman and that men should not judge it too harshly. But this is surely not what she means to say.
Once you understand this, you can see sarcasm pop up everywhere in the poem. For example, the first three lines of the poem say that she is not talented or smart enough to write about elevated things such as wars and kings.
Perhaps the most clear cut example of sarcsasm comes in the following line where Bradstreet claims that women are inferior to men:
Men can do best, and Women know it well.
Preeminence in all and each is yours
Given the fact that she is a woman trying to write good poetry, this is clearly sarcastic. If she believed this, she would not be trying to write poetry.