Reference node table from file datasource

I am using search_api, search_api_solr and search_api_attachments.

I am indexing 3 entities: nodes, paragraphs and files.

I have created a Facet using the node Group title (field_node_group:entity:label). This lists the group titles from nodes in the search results.

node->group title->facet

However, I would also like the group titles from the files to be listed in the facet as well.

I have read up on hook_search_api_query_alter() and it does not appear to be designed for this task, at least with Solr searches: https://www.drupal.org/project/search_api/issues/2619882 →

Programmatically, from the file id I can retrieve the node (parent entity) it is attached to in order to retrieve the title of the group they belong to.

My question is: Is there a hook that would allow me to insert a value into field_node_group:entity:label so that it would appear in the facet results for relevant files in the search results?

In other words:

file->node->group title->facet