How is this character useful as an ally in Curse of Strahd?

Question

As part of the Tarokka card reading, this is one of the possible allies (under Strahd's Enemy, p. 17):

A. Tempter (Queen of Diamonds)
I see a child-a Vistana. You must hurry, for her fate hangs in the balance. Find her at the lake!

This card refers to Arabelle (see chapter 2, area L). She gladly joins the party. But if she returns to her camp (chapter 5, area N9); her father, Luvash, refuses to let her leave.

However, both of the other sections this references, area L and area N9, do not mention anything about how this character could be useful to the party, given that:

she's a seven-year-old girl with no stat block to imply that she's a combatant, not that I'd expect that of this character, or that she has any powers or knowledge or anything.

This character isn't stated to be able to help the party at all against Strahd. Is this something for the DM to come up with by themselves, or am I missing something?

Answer 1

This character is not entirely useless

While you are correct that in most combat situations this character is not very useful, given their stats (chapter 2, area L):

Tied up in the boat is a seven-year-old Vistana named Arabelle (LN female human commoner with 2 hit points and no effective attacks)

As pointed out by Theik, being a Vistana does means she could have access to the Vistani Curses (although at 2 HP a psychic backlash will likely just outright kill her) and Evil Eye

However, the NPC that is chosen as an ally always gains this ability (chapter 1, Strahd's Enemy):

This NPC, whoever it ends up being, gains the following additional action:

Inspire. While within sight of Strahd, this character grants inspiration to one player character he or she can see.

So while probably not one of the best allies to have, this character can still be useful under these specific circumstances, fulfilling their role of helping against Strahd.

Answer 2

"Strahd's got an enemy; that's not the same thing."

Forgive me for paraphrasing Nick Fury from Avengers: Age of Ultron, but I just couldn't resist.

One of Strahd's goals is to find a successor. And, while almost nobody is aware of it from the outset, Arabelle is a viable candidate.

She's descended from Madam Eva, Strahd's half-sister on his father's side.

That said, she's still a Vistana and they're all dangerous. Arrigal, her uncle and namesake, is a CR 8 assassin with delusions of grandeur. Madam Eva is even more powerful. And then they can curse the players.

Mechanically, she's all but useless unless Strahd is present. Think of having her around as a challenge. It invites more opportunities to have Strahd show up and test the party for a bit. This immediately gives her something to do and puts her relationship with Strahd front-and-center. And if the players pull on that thread, they won't be bored.