I feel think about every possible way about this.
For one thing, iNaturalist posts should usually be about the interaction between a wild organism a person. In this case, the person who had that interaction was your mother, not you. Considering this, these might be suitable for Legacy Accounts, which don’t exist now but there’s a Feature Request for them ( https://forum.inaturalist.org/t/create-legacy-account-setting/59623/17 )
Then there’s the large uncertainty about when and where the shells were actually collected. Not good. There could be some value in demonstrating that the organisms did live there at one time, I suppose.
One possibility would be to find a nature center or school or club that might use these, perhaps for education. (I’d like to find such a place to donate the shells I got over a two year period in a small Polynesian country!)