Aloha! You're speaking to Dr. Michael Salkin
I'm sorry that your question wasn't answered in a timely manner. Which breed is Lily, please? Has a urinary tract infection been ruled out? I see that Cushing's has been tested for - ostensibly because overfilling of her bladder has been considered as the etiology of her urinary incontinence. Have other causes of polydipsia/polyuria (increased thirst/increased volume of urine and, hence, overfilling of her bladder) been ruled out - diabetes mellitus
, chronic hepatic or renal insufficiency, Addison's disease, diabetes insipidus, hyperthyroidism, electrolyte imbalances in calcium, sodium, potassium, pyometra (uterine infection in an intact female)?
Can you upload a copy of her test results to our conversation? I understand that you might not have a copy of the results at home but her vet should be able to give you one which you could scan into your computer and give me the link or you can photograph the page(s) and upload the images by using the paperclip icon in the toolbar above your message box (not if you're using the chrome browser) or by using an external app such as imgur.com or dropbox.com.
Finally, if all other causes of urinary incontinence have been ruled out, adding PPA (phenlypropanolamine) to her estriol might do the trick.