I think she's a sable only. the thing with brown/sable dogs is the fur is not just one shade of brown and most of the undercoat is more of a gray color and I think that's what you are seeing. Based on the very dark brown strip on her back and tail, I'll guess her coloration as an adult will be a lot like
my girl. You can also look through other puppy threads here- there are lots of puppy pix to compare the color as they grow.
the magic of the merle is it's very obvious in a small puppy and becomes less obvious as the fur grows in.
I have a sable merle and a sable- not sure how many puppy pix I have of her (the sable) though.
tiny
smerle puppy
vs
regular sables and tris
8 week smerle boy
pic 1
pic 2
pic 3
9 weeks
pic 1
~4-5 months
pic 1
pic 2
~8-9 months
pic 1
pic 2
adult coat
sable girl
~
7-8 weeks
sable merle in the back and sable girl in front- the day that I brought her home at ~10 months
adult coat