just visited this thread today, so your questions may have been answered, but I will add a tad (just cant help myself,
). The marshmallows that we add to our cups of cocoa, were named after the herb, the marshmallow. The marshmallow is a tall plant with a long root that grows in marshes, and Doctors (think 19th century) use to cook juices from the root, along with egg whites and sugar, and whip that mixture up into a foamy meringue that hardened as it sat. That hard piece was considered a medicinal candy and was given to kids to soothe their sore throats. It became very popular with adults as well as kids and later, with manufacturing advances, was developed to the point where the marshmallow herb was no longer needed to make marshmallows.
so todays marshmallows are just the candy and have no healing herbal ingredient.
As for what the herb does, as an herb it helps stop coughing and it sooths throat irritation. If you can find it here (sometimes it is hard), you can make a tea with it using 1/2 to 1 tsp. of crushed root per cup of water, steeping 10-15 minutes. Other than this use, I know of none for this plant, or see a soapy benefit. I suppose there could be some, but I would have to do additional research to know, last I did research, this was it.