Pure lavender water has great relaxing properites and was widely used as a headache remedy in theis era.

Possibly, Elinor carried to the party a vinaigrette, a tightly sealed small box which contained a bit of gauze soaked in lavender water- contents were meant to be sniffed at to revive some-one feeling faint.
A vinaigrette was small enough to be kept in a reticle.

There is a picture of a silver vinagrette at http://www.georgianindex.net/Reticle/Chatelaine.html

'Martha left you her best Love,..., she has nevertheless desired me to ask yu to purchase for her two bottles of Steele's Lavender Water when you go into town.'

- Jane Austen to Cassandra. Jan, 1801.