Did I put my dog to sleep too early ?

She had stopped walking six months prior,....i rescued her from a shelter 15 years ago,.....she pooped and peed where she laid an i did laundry 3 times a day changing her linen. She ate, she drank well,........still reacted with affection. But blood work showed her liver was failing, when I bathed her her hair would just fall off I turned her through out the day but she had losses of hair where her joint were,. i dont feel like she was in any pain though,. her limbs were just dangling appendages so she was around 16 ,.... i had her put to sleep and cremated I feel she may have had a few more months of life without pain Q: did i put her to sleep too early ?