I am a second wife and fear being divorced because the first wife is pressing for it. What are my rights?

You are a lawful wife with full rights, and pressure from others for you to be divorced is forbidden in the hadith. The Prophet ﷺ forbade a woman to ask for her sister's divorce — this prohibition applies in both directions. If your husband does divorce you, you are entitled to ʿiddah maintenance, mutʿah (consolatory gift), and other rights like any divorced wife. Make sure the marriage is registered so that these rights can be claimed in court. Try to be patient and conciliatory, because such pressure usually comes from pain, not merely hatred. See prospective second wife.