I have a girl who is 4, and I got her spayed recently. I'll try to give you advice from my perspective.
Dogs go into heat starting one week in (no blood), one week bleeding, and one week going out (again no blood). It is the 3rd week that usually is the easiest time to get preggos. At 8 months, she is on the early side of going into heat. My Uni didn't get her first until 13 months! Yes, the vjj will be swollen, and yes she will be licking a lot. Diapers just aggravate them more, and yes she was oh so moody and clingy. I don't think waiting until 2 1/2 years to spay is a good idea. Each and every heat they get they have a chance of pyometra.
Pyometra - Wikipedia, the free encyclopedia
Also if you spay early there is next to zero chance of her getting cervical and other types of cancers. The reason why I didn't get Uni spayed earlier was I didn't find a vet I was comfortable with until recently, and now that we did it, it was the best decision I ever made. Spaying around 8 months is good for small dogs imo, they get a chance to get a bit bigger, and wait out if any baby teeth don't fall out. Get the teeth pulled at the same time as the spay. Oh and get a softee cone for after the spay, so much better than those horrid plastic things.
The food you are feeding is a good high quality food, I'd try to keep her eating that. When she vomits, is it yellow foamy bile? That may mean she is hungry but holding out (from my experience with Uni). And most dogs crunch just a bit then swallow the rest whole. I would try to get her to eat her regular food, and after she's eaten then give some treats thruout the day, but healthy ones, like fruits and veggies, egg white, chicken bits, etc. Please no ham, hot dog, bologna, etc, too fatty and salty. Yorkies already have high fat in their blood, susceptable to pancreatitis (Uni has this).
Female dogs are more likely to have uti's and if you suspect she may have one, bring her to the vet and have a urinalysis done. Extreme case it could lead to crystals or even bladder stones.