The McGonagall problem.
We know that Isobel married a muggle and named her daughter Minerva McGonagall after her own grandmother.
Most probable explanation.
1880 Minerva Mcgonagall 1st is born.
1898 after graduating from Hogwarts, she married a wizard.
1899 had a daughter, and her husband died. She stuck to her maiden name.
c. 1907 started teaching at Hogwarts.
c.1911 chased a young Leta down the Hogwarts ground.
1917 became a grandmother. Her daughter had a daughter, named Isobel , with a wizard, Mr. Ross.
1927 threw shades at some interfering ministry officials.
1935 became great-grandmother as Minerva McGonagall 2nd, the one we know so well, is born.
6 Oct. 1935.
Minerva McGonagall 1st : Dumbledore, I am resigning. I feel old and tired now. I became a great-grandmother two days back.
Albus Dumbledore : well, that's good news, but you being old? Nonsense! You don't look a day over 20.
Minerva : (smiling weakly) Isobel is naming her daughter after me. Everyone was against her marriage, but I secretly supported her.
Dumbledore : so, she'll be named Minerva McGonagall! I bet she'll be talented like you. and make even more delicious chocolate fudge than you do.
Minerva : (trying to smile) I think that muggle boy, Malcolm, will keep her happy.
Dumbledore : He is a McGonagall like you. Is he some distant relative of you?
Minerva : (finally crying) I don't know! I lost all contact with my former family. I had chosen the wizarding world for me! Sometimes I think that I should've....
Dumbledore : now! now! We can never reverse our choices, so why fuss over them!
Minerva : maybe you're right. But I'm thinking of Isobel! She chose the muggle world for her!
Dumbledore : The road to wizarding world is never closed for any witch or wizard.
Minerva : anyway! I handed my resignation letter to prof. Dippet yesterday. I need a free life and care for my health now. Don't worry! I'll keep sending you specially made chocolate fudge, and Honeydukes' best sherbet-lemon.
Dumbledore : oh! So you know I am fond if them. Muggles do know how to make candies! 😊
Minerva finally smiled!