I have looked everywhere but can't find a clear answer to this question. I found this site:https://ell.stackexchange.com/questions/6372/when-is-the-past-perfect-exactly-needed that says:
The past perfect is optional [i.e. may be replaced by past simple] only when talking about an action at a specific time.
My sentence is 'The girl who had walked her dog is my sister Claire'
Can I omit 'had' and make the sentence 'The girl who walked her dog is my sister Claire' but is it correct to use either with 'to be' in the same sentence.
I can only find information on using 'had' and 'to have' in the same sentence from this site: https://www.really-learn-english.com/had-have-in-the-same-sentence.html
Grammatically, you can combine HAD and HAVE when making a verb in the present perfect verb tense.
"I have had lunch already," which means you already ate your lunch before now.
But no matter how much I search I can't find examples of past perfect and present tense in the same sentence.
Can someone please point me in the right direction?