This may be just a philosophical question. I found a couple of conversations in the past discussing this topic and I wanted to ensure the question was clarified to get better feedback on the context for posing my question.
Thread 1 and Thread 2
I saw a lot of great positions for using past tense in general when one or both of the people were dead. However, in this context, I am only asking to think about the parent-child relationship aspect of the question.
I also saw a lot of great positions for stating the relationship without using the verb, and I think that is fine as well. But I have run into times when the sentence gets a bit long depending upon the other facts I'm trying to get into the paragraph. But I will look for opportunities to use that format when it does not get cumbersome.
When I think about the parent-child relationship specific to genealogical studies, we are all striving to prove the relationship between them. When Mary gives birth to Polly, there is a genealogical relationship that will never go away. They will ALWAYS be linked regardless of their stage in life after birth. Therefore, since our primary task is to define those relationships, it would seem that the relationship transcends death. Polly is the daughter of Mary from a genealogical perspective. If I say Polly was the daughter of Mary, then who is she the daughter of now? I can't say no one, as she would therefore not exist. So it would seem that Polly will always be the daughter of Mary, regardless of the living status of either one.
Certainly, I can use the past tense for either one of them in just about any other context, i.e., my mother was a seamstress, my father was a farmer, my daughter had blue eyes. These are all states that change through life. But the fact of their linkage through birth will not.
Of course, I truly don't think any reader of these profiles will be confused by any of the three uses mentioned, but I'd still love to hear other opposing or supporting opinions to my thinking because you never know what you don't know.