As a parish organist I am often asked to include secular songs which the family chooses because they held special significance for the deceased. I explain that these songs are not appropriate, but the requests continue. Do such songs have a proper place in the Funeral liturgy?
The introduction to the Order of Christian Funerals devotes four paragraphs to the question of Music in the Funeral liturgy (numbers 30-34). Number 30 is particularly relevant to your question.
"Music is integral to the Funeral rites. It allows the community to express convictions and feelings that word alone may fail to convey. It has the power to console and uplift the mourners and to strengthen the unity of the assembly in faith and love. The texts of the songs chosen for a particular celebration should express the paschal mystery of the Lord's suffering, death, and triumph over death and should be related to the readings from Scripture."
Thus, while Funeral music may express "convictions and feelings," its subject must always be the paschal mystery and it must be related to the readings from Scripture.
Rather than adopting popular secular songs which are inappropriate to a liturgical setting, we should seek out good liturgical music on a paschal theme which can "support, console, and uplift participants and help to create in them a spirit of hope in Christ's victory over death and in the Christian's share in that victory." (Order of Christian Funerals, number 31)