Is my targeted client’s dog suffering physical health problems induced by the interlopers, in order to make the owner miserable by destroying this source of comfort and love she depends on?

This is not the case. The reason being, as you are seeing intuitively, that it is hard for the extraterrestrials to imagine the importance of a love bond between a human and a companion animal. The most they can identify with the idea of pet ownership is having a somewhat interesting object that is acting independently, over which one must exert power and control so it presents a kind of challenge to manage them but is good practice for life in that respect, and this, of course, is the most shallow kind of relationship one can imagine with another being, whether human or not human. So they simply give little or no weight to the value of the animal companions and would rarely use that as an opportunity to punish someone. Nothing can be ruled out when it comes to savagery, but it is not the case with your client that this is happening.