"Yeah! I made a friend!" she announces rather loudly and gestures towards Harriet.

This is news to Harriet!

Hagrid glances at her.

"Well, we've got lots still to buy, so Harriet and I oughta get going."

"Don't let me stop you."

"Bye Harriet! See you at Hogwarts!"

A bit shyly: "See you later, Serpens..."

And onward?

Onward.

As they walk down Diagon Alley, Hagrid glances at Harriet again and says, "Did she, er, tell yeh who she was?"

"She said her name was Serpens Malfoy. And that my mom got her dad sent to prison..."

"Her dad was named Lucius Malfoy.  After your mum got rid of Voldemort, a lot of the Death Eaters in Britain got found out, and he was one of 'em.  Narcissa, that's Lucius's wife, she says she never knew anything about it."

"Oh."

"Serpens said it'd only be a problem if he got out..."

Hagrid does not look like this makes him feel better.  “What did she say to you, exactly?”

"Uh. That he'd be mad and out for blood, and then she said she thinks we'll get along great..."

Hagrid thinks about this.

“Well,” he says, finally, “just ‘cause she says you’re friends don’t mean you have to hang around her if she makes you - uncomfortable.”

"She was weird? I dunno she made me uncomfortable though..." She shrugs.

“Well, all right,” he says.  “But there’s always plenty of people to meet at Hogwarts, don’t forget.”

She nods, slowly.

"Right, then, what's next?"

Potions supplies is next, a pewter cauldron of "standard size two" and a miscellany of tools for preparing and measuring potion ingredients, phials and tablespoons and a special sort of knife called an athame.

She seems interested when it comes time for buying books, looking around the shop with wide eyes, staring at colorful moving displays and books.

Wizarding books are just as strange as wizarding clothes!  Great and heavy and dusty, or tiny and delicate, titled in runes or syllables, bound ornately in metal, padlocked...

Her textbooks are relatively ordinary, as far as they go, but still decidedly eye-catching by muggle textbook standards.

"You like books, Harriet?"

"Yeah..." she says, voice a bit soft.

"Well, I got enough gold out from your vault for you to get a couple things for yourself, if you'd like.  Though some of these books've got spells it'd be dangerous for you to try, least for a while yet..."

"I can avoid any unsafe books."

"You're a smart kid.  Anything with advanced spells - you'll want to stick to starter stuff at first, 'specially your very first year.  An' potions can go badly wrong if you try 'em outside the classroom.  But you'll learn all about that at Hogwarts.  Let's take a look around, shall we?"

"Okay!"

She doesn't actually gravitate to anything with spells in it - she wants the magical bestiaries, and the history books, and the books on other countries...

Hagrid's grin gets especially crinkly when he watches her fawning over magical bestiaries.  He pays.

"Right," he says, "next is your wand.  And you should have your own luggage, too."