The speaker is angry, and she is tired of being told that her anger doesn't count. The poem opens with a question about why her feelings get "reduced," then lists the excuses people give: she's a woman, so it must be hormones; she's young, so she must know nothing. Each reason treats her anger as a mood or a tantrum rather than a response to something real.
Halfway through, the poem turns with the word "But." She says her anger is "calculated" and "not hurried," built on learning and on having "seen the horrors of the universe." The repeated "I have a right" lines sound like a steady, deliberate argument rather than an outburst, which proves her point. The final line, though, admits the cost of being ignored: not being heard only makes her angrier. The mood is frustrated and defiant, with a controlled determination underneath.