We feed TOTW, and have done amazing on it! I thought it might be too rich at first, especially since my dogs are so low energy, but no problems. I think we have been feeding it for 2 years now (?), pretty sure. I guess we are just lucky.
Also, I noticed you said one of them was 10lbs. My chihuahua X is 9.5-10 lbs, and is definitely not overweight. You can see her waist line, and feel her ribs under a thin layer of fat. Chihuahuas have a large size range (mostly due to byb's and puppy mills), but you should be able to tell if they are overweight. It sounds like they are based on the description you gave. I would tell her about all the health problems dogs can develop from being overweight. If she really loves her dogs, I don't think she would want them to become ill from something preventable, like being overweight. That's the only way I can think to get through to her. Good luck!

Also, I noticed you said one of them was 10lbs. My chihuahua X is 9.5-10 lbs, and is definitely not overweight. You can see her waist line, and feel her ribs under a thin layer of fat. Chihuahuas have a large size range (mostly due to byb's and puppy mills), but you should be able to tell if they are overweight. It sounds like they are based on the description you gave. I would tell her about all the health problems dogs can develop from being overweight. If she really loves her dogs, I don't think she would want them to become ill from something preventable, like being overweight. That's the only way I can think to get through to her. Good luck!