The agent (the person who has Power of Attorney) is allowed to conduct business and financial transactions for the principal. This would entail selling an automobile. But, the agent also has a duty to act in the best interest of the principal. Any such transaction must survive the scrutiny. While it would be permissible for the agent to sign over title to your husband, since it is close in the family like that, it may look a little suspicious. I think you could sufficiently cover your bases by having the costs to repair estimated and then you would have proof that it would not be worth fixing. However, giving it away could be considered to not be in the best financial interest since you could at least sell it and at least get something out of it. Something is, after all, better than nothing. But if your husband is willing to fix it himself, I think it would be reasonable to give him the vehicle as compensation for the repairs since that would have saved your mother the expense of fixing it up in order to sell it. Just document everything including parts and labor and have it estimated in order to protect yourself just in case someone would say that you are tryinjg to take advantage of her. Best of everything.
I would agree with Attorney Austin's response. The one other potential argument in your favor, if someone were to challenge this transaction, (it is not clear from your summary whether or not there is someone who might do so), is that by transferring the vehicle, you are eliminating an expense or potential liability for your mother, in terms of insurance, etc.
If you believe someone might challenge this, you can always petition the court to approve it.
Best of luck to you!