Could have.... could be

Mother: Oh, my Karen, my baby, all grown up. I so wish your father could have been here today. I wish he could have seen you.

I don’t understand why she used “could + have + past participle” in the situation (her daughter’s wedding).
I thought the sentence would or should be like,
“I wish your father were here.” Or
“I wish your father could be here”.

I’m confused now.

I’m not a language teacher but when someone says “I wish X could have been here.” it implies there is an unavoidable reason that they are not there. It does often get used when the person that cannot be there is dead. It may be this way as the subjunctive but don’t quote me on that.
‘I wish your father was here’ and ‘I wish your father could be here’ are also perfectly valid.