What should I do about an Emirati citizen's marriage proposal, knowing that I am recently married and have a child, and she is offering financial assistance in exchange for my marriage to her without my wife's knowledge?

If you are able to provide for and be just between your two wives, then marry this woman as an act of kindness and to preserve her chastity. It is not a condition for your first wife to know or to consent, though that is preferable. The conditions for a valid marriage must be met: the guardian (wali), the dowry (sadaq), and witnesses. Publicizing the marriage is not a condition, though it is better. The second wife may waive some of her rights, such as financial support (nafaqah (definition)) and overnight stay (mabeet).