Hi
Welcome to Yorkie Talk.
Her vaginal area being swollen is a normal part of the heat cycle. The whole cycle takes aprox. 3 - 4 weeks, but parts of it you may not notice (she still can get pregnant though).
There are doggie diapers you can buy at any Petco or Pet-Smart etc that are made of cloth and velcro and most of them you just put a maxi pad in them.
You can gently clean the area a few times a day with a warm wet papertowl or washcloth.
I'm sure you already know this, but 110% keep her away from any un- neutered male dogs of ANY age until you get her spayed. Even though she's young she can still get pregnant and any un-altered male (even a very young one) can cause that.
And do the spay ASAP, the longer you wait, the more heat cycles she'll have, the more intense (and more expensive)the surgery.
If you need further advice, check the "breeders" section, they obviously are very experienced.
