With our rescue, that would mean that you were the legal owner of the dog. The only way that they can take him back is if you have violated any written agreements within the contract ie abused the dog or whatever they might have written as conditions.
There is no take back clause, just one saying that if we can't keep him we must return him to them. Yeah, tried that and this is what resulted. We have not violated any terms of the agreement.
I also wonder about the structure of that particular rescue, because you said that it is the foster making the threats. In our rescue, all the fosters do is foster. They don't make any decisions or have any power (so to speak). The coordinators decide who gets to adopt the dogs - not the foster homes. We also have a board of directors who make the major decisions.
I'm hoping that the rescue that you are dealing with is the same. Maybe the foster is just venting her opinion but really has no say in the matter.
The fosters can decide to whom the dog is placed. Very loosey goosey organization.
I really think if you can just convince her that Tucker is happy, safe and loved with you, that it will all be fine.
Sorry, but no that will not work. They are being 100% unreasonable and fabricating their own truths. Besides, that animal law attorney cautioned to have no further communication with them since the threat of a lawsuit was thrown out by them today. The ball is in their court.