in the Curse of Strahd Adventure, you learn from reading an ally's tarokka card which is intended to help you against Strahd. These possible allies are listed on pages 15-17 under the Enemy section of Strahd.
This ally often does not know it and must be convinced or at least informed of the reading of the tarokka card before wanting to join you. This is mentioned either as part of their description on pages 15-17, or as part of their description in the area where you meet them for the first time. As examples, the book describes:
This map refers to Ismark Kolyanovich (see chapter 3, zone E2). Ismark will not accompany the characters to Castle Ravenloft until he knows that his sister, Ireena Kolyana, is safe.
– p. 16, Strahd's enemy
This map refers to Clavin Belview (see chapter 8, area S7), the two-headed mestizo. Clavin serves the abbot out of fear and perverse loyalty. His job is to deliver food to the other half-breeds, whom he abhors. If the abbot still lives, Clavin does not want to gain the wrath of his master by trying to leave, and he refuses to accompany the characters. But if the abbot dies, Clavin has no reason to stay in the abbey, then he is ready to come if he is bribed with wine. Clavin offers no advantage to the party without its violation.
– p. 17, Strahd's enemy
If your card reading reveals that Sir Godfrey is Strahd's enemy and the characters persuadingly ask him for help, he offers to join the fight against the vampire. Fate has unlocked his memory of the love he and Vladimir once shared, and the power of that memory prompts Godfrey to help fight Strahd and restore the honor of order. (…) Although Sir Godfrey is not aware of the reading of the tarokka card, he somehow feels that he must do one last task before his mind rests with Vladimir, and he therefore accepts to help the characters face Strahd at Ravenloft Castle.
– p. 139, Ravenloft Fortunes
However, there is one ally in particular for whom there does not appear to be an exact description of how this character becomes your ally (there could be other allies who do not receive a description of how they become your ally, I didn't do an exhaustive search for a description of each possible ally; I know there are some who will obviously help you, like Ezmerelda, and therefore don't no need for a specific description of what it takes to convince them, but the ally I ask question is not as obvious):
B. Tempter (Queen of Diamonds)
I hear a wedding bell, or maybe a death knell. He calls you to a mountainside abbey, where you will find a woman who is more than the sum of her parts.
This map refers to Vasilka the flesh golem (see chapter 8, zone S13).
– p. 17, Strahd's enemy
Zone S13 can be found on pp. 150-151, and the entirety of its description (ignoring the "boxed text") is as follows:
The woman in tattered red dress is Vasilka, a Flesh golem who was wonderfully set up to serve as Strahd's wife. Figures within 5 feet of Vasilka can see the seams in his powdery skin where disparate body parts stolen from Krezkite graves have been carefully sewn together.
The abbot teaches Vasilka the intricacies of etiquette. He also intends to teach her to dance. Vasilka obeyed all of his orders. She cannot speak but lets out an impious cry if she is hurt. If she is mad, she fights until the abbot regains control or until she is destroyed. It has the supernatural strength of a typical flesh golem despite its small size.
– p. 151, S13. Main hall
Unless I forget something, there doesn't seem to be any guidance given to the DM on how such a character would become the party's ally against Strahd. Of course, as DM, I could come with Something, but I would prefer to have information on the possible advice of the adventure, because currently I do not know how I could give a narrative sense to this.
Are there any indications that I have ignored on how this character becomes the party's ally against Strahd?