Doll lips sounds specific. It isn't. None of the sources LookPrep cites describe a technique of its own under that name.
InjectCo uses it for cherry-style fullness in the centre of both lips plus a defined Cupid's bow. The IV Lounge uses doll-like wording for cherry lips. Russian lips get the word "doll" attached too. So two people can say the same name and picture different mouths.
What helps is splitting the look into the two features it seems to be made of:
Answer those separately and you have something an injector can work with. Bring a reference image if you have one.
Two more things worth knowing before the consult. The sources give no doll-lips amount and no duration for this look. And the side profile isn't described at all, so ask to see comparable side-view results rather than guessing from a front photo.
If you want to compare the outline and the fullness on demo faces, LookPrep shows what doll lips filler looks like as an illustration, next to cherry, Cupid's bow and Russian lips. The frames are drawings to talk through, not results.
Sofia R., LookPrep