Why don't you stick with just the molasses for now? Try to get the rest of it down her. Tomorrow you can try the Epsom salt flush if there isn't any improvement.
Yes, Epsom salt is a very good flush. Molasses is, too, and may be easier for the chicken to drink on their own. But some will readily drink the Epsom salt solution, too. If not, you will need to syringe or tube it into the crop.
If you do the Epsom salt flush mix one teaspoon of the salts with...
Yes, follow up the oil a day later with one teaspoon of molasses mixed into one-fourth cup warm water. The chicken should drink it all, so leave it as the only water source until it's gone. Or you can syringe it into the beak.
The easiest way to put oil into a chicken without it getting all over you and the chicken is to measure out a teaspoon of coconut oil, then divide it into pea size pieces, then chill them until they are solid. Pry open the beak and slip them into the mouth one at a time. The chicken will easily...
Reflexive vomiting points to obstruction. Introducing oil and/or a stool softener can help. A molasses flush can help clear out the remaining material stuck in the gizzard following the oil treatment.