Planting a Placenta and Ashes together, Is it Tapu

My husband's mother passed away a year and a half ago and his stepdad still has the ashes but plans to scatter them in the ocean later this year. We would like to take some of the ashes and put them in a big pot with our baby's placenta, but someone told me they thought it was Tapu? I have looked online and can't find anything that says otherwise. Does anyone have any info on putting ashes and placenta together?