Sarah slides the letters under the bed and puts away her clothes in the wardrobe. Then she'll go do chores and live her life normally until something upsets her routine.

It's almost like she's prescient.

Uncle Vernon is reading when there is the sudden sound of an extremely loud motorcycle followed by a pause and a somewhat less loud, thunderous knock on the door, like someone hit it with a tree, causing him to startle bad enough to knock his brandy over.

Sarah allows herself to look surprised but otherwise doesn't react.

Petunia walks over to the door and opens it—

—and nearly faints on the spot. "V-Vernon!"

On the other side of the door there is the largest man Sarah has ever laid eyes on, his head nearly completely obscured by a shaggy mane as black as his eyes. "Good evening! Mighty hard ter walk around here without bein' noticed."

This seems plausibly related to the magic people. Sarah is looking forwards to this. "Hello."

"P-Petunia! Stand back!" he cries, interposing himself between his wife and the giant man.

Dudley shows up from upstairs to see what all the ruckus is about and squeals in terror when he sees the man.

"Well, did no one ever teach yeh manners? Aren't yeh gonna invite me in?" And without waiting for an answer he squeezes through the door and closes it behind himself. He's carrying a large purple umbrella in spite of the complete lack of rain outside. "So. Yer Sarah, eh?"

"I am. It's nice to meet you. May I ask your name?"

"I'm Rubeus Hagrid, Keeper of Keys and Grounds at Hogwarts."

"I will not have that name spoken in this household!" Uncle Vernon says, going red in the face.

Sarah thinks, it's probably better that the Dursleys don't know she sent a reply if she can avoid it. "Are you here to talk to me then? Perhaps it would be better if we spoke elsewhere. My uncle can be very passionate at times."

"Oh no, we should talk to him, too. What name? Mine?"

"No! That—that other one."

"...Hogwarts?" He blinks, then looks at Sarah. "Did they ne'er tell yeh?"

"They prefer not to talk about my having magic."

"Don't say that word! Not in my house!" He puffs out his chest, faces Hagrid down—up—and says, "I demand that you leave my property at once!"

"Ah yeh do? And what'll a great muggle like yeh do about it?"

Sarah is not going to interrupt the two arguing adults.

Uncle Vernon doesn't seem to have anything to say to that.

And Petunia seems to just be frozen in horror.

"So! Sarah!" he says, making his way to the sofa and sitting on it, causing it to groan dangerously.

(Petunia makes a very similar noise to it when that happens.)

"What would you like to talk about?"