Nisan is the month of Pesach, the holiday celebrating our freedom from Egypt. It’s the beginning of spring (though not necessarily in England), a month of renewal and rebirth.
The custom, therefore, at a funeral during Nisan is to not give a full hesped, eulogy. Although the funeral is a time of grief for the family, the hope and optimism that this time of year naturally awakens partially override their obligation to mourn.
One may, however, speak briefly about the good qualities of the deceased. In describing eulogies in general, the Shulchan Aruch writes that “it is a great mitzvah to eulogise the dead person appropriately. And the mitzvah is to raise one’s voice to say over [the departed] things that break the heart, so that there will be much crying; and also one should mention his good deeds”.
We do not give an intensely emotional eulogy that will bring people to tears during Nisan, but we can praise the good in the dead person and inspire others to follow in their footsteps.