S.H.
Let her sleep with something of yours, that you have worn a lot and that has your smell on it.
Does she have a lovey? If not, try to see if she will gravitate toward one. My son for example since 6 months old, loved to sleep with his stuffed cow.
The previous poster, MechanicMama also gave some commonly used alternatives.
Perhaps also, instead of nursing her before sleep.... feed her from a bottle before sleep. Instead. Either your pumped milk or whole milk etc.
Most kids/babies... nurse/drink milk before bed. It is soothing. And there is something in milk, which naturally calms a child.
Where does she sleep? In a crib? Co-sleeping?
Any transition, may take time. So, keep that in mind.
all the best,
Susan