How could Dumbledore have prevented Kreacher from joining Bellatrix if she was his mistress?

Question

In Half-Blood Prince, Dumbledore summons Kreacher and explains to Harry that the elf may have been inherited by Bellatrix Lestrange. It is possible that Dumbledore simply captured Kreacher after the death of Sirius.

Dumbledore then asks Harry to give him an order, and says something peculiar.

“Give him an order,” said Dumbledore. “If he has passed into your ownership, he will have to obey. If not, then we shall have to think of some other means of keeping him from his rightful mistress.”

Of course, it immediately becomes clear that Harry was the new master of Kreacher.

However, if Bellatrix had been his new, "rightful" mistress, she would have, sooner or later, entered 12, Grimmauld Place (which she had inherited) and, not finding Kreacher, she would have ordered him to come back home.

This would have been a problem for Dumbledore, because we know that

“The house-elf’s highest law is his Master’s bidding,” intoned Kreacher. “Kreacher was told to come home, so Kreacher came home...”.

It should be pointed out that Kreacher managed to escape from a cave on which Voldemort himself set up an anti-Disapparition jinx, simply because his master told him to come home.

Dumbledore likely knew that house-elves magic is very powerful, that they can easily Disapparate, and that they do everything they can in order to obey the orders of their rightful masters. Yet, he hinted that there may be ways to keep Kreacher away from Bellatrix.

As such, a question arises:

How could have Dumbledore prevented Kreacher from joining his rightful mistress?

I know that Dumbledore is extremely powerful, but I'd like to know if there's any canon source which suggests spells or other techniques which Dumbledore could have used in this case.

Answer 1

He probably intended to use a memory spell

Dumbledore probably would've manipulated Kreacher's memories: either wiping out all the elf knew about the Order, or convincing him that he belonged to Harry or to Hogwarts. Maybe even made him forget his own name and the Black family. There is no canon information how memory charms affect the bond between the elf and his owner, but if Kreacher forgot his own name, there is a good chance his mistress, Bellatrix couldn't have summoned him.

Dumbledore is not above using spells to affect the perception of those who would not submit to his will: he used a spell to confound the manager of Wool's orphanage, Mrs Cole:

There was no doubt that Mrs. Cole was an inconveniently sharp woman. Apparently Dumbledore thought so too, for Harry now saw him slip his wand out of the pocket of his velvet suit, at the same time picking up a piece of perfectly blank paper from Mrs. Cole’s desktop. “Here,” said Dumbledore, waving his wand once as he passed her the piece of paper, “I think this will make everything clear.” Mrs. Cole’s eyes slid out of focus and back again as she gazed intently at the blank paper for a moment. “That seems perfectly in order,” she said placidly, handing it back. ~Harry Potter and the Half Blood Prince - The Secret Riddle

also when Dumbledore was collecting information about Tom Riddle, when he extracted memories it wasn't always with the full cooperation and approval of the subject. He had no scruples to invade someone's brain if needed, I don't imagine Morphin Gaunt, for one, was very cooperative:

“But he had this real memory in him all the time!” “Yes, but it took a great deal of skilled Legilimency to coax it out of him,” said Dumbledore, “and why should anybody delve further into Morfin’s mind when he had already confessed to the crime? However, I was able to secure a visit to Morfin in the last weeks of his life, by which time I was attempting to discover as much as I could about Voldemort’s past. I extracted this memory with difficulty. ~Harry Potter and the Half Blood Prince - A Sluggish Memory

Memory charms frequently used in the wizarding world, they even have an occupation called 'obliviator': professionals used by the Ministry of Magic to modify memories. Dumbledore, if necessary, would have used a spell to obliviate or confound Kreacher to protect the Order, presumably preferring this solution to imprisoning Kreatcher - which he also could have done. House elf magic is different, they can do wandless magic and are not affected by the usual anti-apparation wards, but it doesn't mean they can't be affected by magic. It's true that Kreatcher escaped from Voldemort's cave, but it's not because the magic of house elves is unbeatable by wizards, rather because Voldemort thought house elves were negligible - the possibility of Regulus Black's house elf escaping hadn't even occurred to him. Dumbledore, on the other hand wouldn't do such a mistake - he was well aware of the consequences of Kreacher joining his mistress, so he'd have taken the necessary measures if needed.

We know house elves are susceptible to mind spells, after all they were subjugated and mentally bound by wizards. A brilliant wizard like Dumbledore, who was also proficient in legilimency and occlumency would have found a solution to affect the mind of Kreatcher if he had no other choice.

He could've convinced Kreacher that his life's ambition was to move to Australia and open a kangaroo farm or any other place out range of the slave-master connection.

Answer 2

Specifically, to answer your question, no, there are no canon sources which suggest spells or other techniques which Dumbledore could have used in this case. I assume you mean to prevent Kreacher from returning to Grimmauld Place. As Dumbledore notes, there are other ways of preventing Kreacher from entering Grimmauld Place at his master's or mistress's command, but I can't find any specific examples of spells or other kinds of magic.

Bellatrix was not Kreacher's mistress; therefore, the magical connection between a house-elf and its master does not exist between Kreacher and Bellatrix. I think what's important to remember is that, according to J.K. Rowling, house-elf magic is different than wizarding magic, so whatever magic Dumbledore would have had to utilize to keep Kreacher out of Grimmauld Place would have at least had to have taken elf magic into account when conjuring magic that would have kept Kreacher (and Bellatrix) out. I.e. Dumbledore couldn't have -- I'm guessing -- just used wizarding magic against Kreacher and Bellatrix; he would have to take elf magic into consideration. How he would have done this is not laid out in canon. But it does demonstrate Dumbledore's ongoing brilliance, what with him possibly knowing elf magic (And, note, I say Dumbledore may know about elf magic; I'm not suggesting I know that Dumbledore knows how to use elf magic. He may. He may not.)

Answer 3

Dumbledore doesn't seem particularly thrilled about the "other means." It could be that these "other means" are as simple as killing Kreacher.