Purchased Tuesday, 2/3/15: Female, 9-wk old, un-spayed, 2-lb pure-breed Yorkie. No incontinence observed. Beginning

Aloha! You're speaking with Dr. Michael Salkin
While a bacterial UTI can certainly cause the urinary incontinence you've noted, it's important to recognize that a UTI may have arisen secondary to a congenital defect such as an ectopic ureter. It's important to culture such dilute urine two days after the course of antibiotics have been completed to make sure that the urinary tract has, indeed, been sterilized. If it has and Darla remains incontinent, ectopic ureter becomes an important differential diagnosis and so ultrasound of her urinary tract is indicated in an attempt to identify such a congenital defect.
Clavamox is a good choice when a culture and sensitivity hasn't been performed. It's nicely broad spectrum. Albon (sulfadimethoxine), however, doesn't have a place in treating UTIs in dogs. Please respond with further questions or concerns if you wish.

Sounds good.
1) No, I'd hold off on blood work and concentrate on the urinary tract for now. If nothing untoward is found either by bacterial culture and sensitivity or ultrasound, we can pursue more unusual causes of urinary incontinence such as overfilling due to polydipsia (increased thirst)/polyuria (increased volume of urine) as seen with a number of metabolic disorders.
2) No, not until the etiology of her incontinence is identified. There's quite a bit of anecdotal information concerning the use of apple cider vinegar but please note there isn't a whit of scholarly study that suggests it's of any value in dogs.
3) No, "immature bladder" isn't recognized in dogs.
I can imagine. What's cuter than a 2 lb Yorkie! Please continue our conversation if you wish. You're quite welcome.

I understand. I don't know what the mechanism of such an "immature bladder" would be, however. The proper sequence to follow with Darla is the following:
1) Complete the antibiotics, wait 2 days and perform a bacterial culture and sensitivity on urine obtained by cystocentesis - percutaneous aspiration of her bladder.
2) If negative for bacterial growth but she remains incontinent, ultrasound her urinary tract in an attempt to identify a congenital defect such as ectopic ureter.
3) If positive for bacterial growth and a congenital defect can't be found, select another antibiotic as determined by the culture and sensitivity. Continue treating for 10-14 days and once again perform a bacterial culture and sensitivity 2 days after the course of antibiotic has been completed.
I can't set a follow-up in this venue and so would appreciate your returning to our conversation with an update - even after rating - at a time of your choosing.

It's my pleasure. Thank you for your kind words and accept. I appreciate it. I hope to hear from you soon.