No never use a slicker on a yorkie ! I used a slicker on Fido when he was a pup and it ruined his coat (he had floor length coat!) so I had to shave him all down
Just use a comb with rotating pins for matts, then you can use a pin brush when the coat has no matts in it anymore.
Brush her everyday, bathe 1 a week but until the puppycoat goes its enough to bathe every 2 weeks and if you think she's dirty.