She is so adorable!
Is this one? - https://www.amazon.com/Science-Diet-Senior-Defying-Chicken/dp/B00E0KFASS
Also, have you ever give her the Royal Canin food specifically made for Chihuahuas? - https://www.amazon.com/Royal-Canin-Adult-Chihuahua-Food/dp/B00IK5SPHM/
If so, do you have any opinion on it? I moved my 2 Chihuahuas from grain-free to grain inclusive food and since the top 3 brands are Hill's, Royal Canin and Purina for scientifically tested and proven dog food .. I had no choice but to pick one from it and give it a try.