8 weeks is VERY young to be bringing home a new puppy. You will find that in most cases, reputable breeders will keep Yorkie pups until they are 12 weeks.
I would search this site and look over some of the problems others have had with bringing home pups this young to better prepare yourself.
For the time being, I would DEFINATELY keep her on the the food she is accustomed to while she is adjusting to her new home. Then, when you are ready to switch her food, do it VERY gradually, feeding less of her current food and more of the newer one.
There are many foods and options out there that are a better quality than the one she is currently on. The trick is, determining which one is best for HER. To do that you will need to research and get a good understanding of what she will need and do trial an error runs to see what works best. There is a sticky at the top of this section with some of the more recommended (YT recommended in any case) brands that you may want to start out with. Some of the companies will send you free samples or coupons if you contact them.
dogfoodanalysis.com is a good site to get information regarding the ingredients in foods, but the "ratings" assigned and information on the site is based solely off the opinions of the site editors, not long term professional research. Don't let your search for info on food start and end with that site--look for info from numerous sources and determine what needs your little one will have rather than just picking something off one person's 'ratings list.'
A few other sites you may want to read up on are:
The Dog Food Project - How does your Dog Food Brand compare? Dog Food Review Ratings
Congrats and good luck with your little one. Be sure to share pictures with us when you can. Welcome to YT!