Welcome to YorkieTalk. I don't have any experience with female Yorkies, but my boys are primarily piddle pad users. Could the collar be preventing your little girl from sniffing the piddle pad?
Some other possibilities/suggestions, if you don't already do these things:
1) always immediately praise when your girl does things right; never stop praising and maybe offer a small treat
2) keep the piddle pad in close proximity for quick access at all times; as long as the potty problems continue, limit your girl's freedom to roam your home. Keep her in one room and watch her closely when you can.
3) change the piddle pad often (my guys prefer a fresh pad for poops
)
4) make sure you completely clean accidents in the carpet with an enzyme cleaner or white vinegar so that your girl won't want to return to those spots
Hope something here helps. Good luck!