Is it permissible for an engaged woman to give her dowry to her fiancé before the dowry is named in front of her family?

It is permissible for a mature, sane, and رشيدة (of sound judgment) wife to waive her mahr (dower) or part of it for her husband after it has been established by the marriage contract, based on the Almighty's saying: ﴿إِلَّا أَنْ يَعْفُونَ﴾ (unless they [the wives] remit it) and ﴿فَإِنْ طِبْنَ لَكُمْ عَنْ شَيْءٍ مِنْهُ نَفْساً فَكُلُوهُ هَنِيئاً مَرِيئاً﴾ (But if they, of their own good pleasure, remit any part of it to you, take it and enjoy it with good cheer and satisfaction). As for waiving the mahr before the contract, it is invalid, because the mahr is not established except by the contract. And if he marries her on the condition that she has no mahr, she is entitled to the mahr of her peers (mahr al-mithl).