I think that "Mrs. Jennings's endeavours to cure a disappointment in love, by a variety of sweetmeats and olives" and also dried cherries are just Mrs. Jennings trying to be kind in any way she can and not actual remedies, but there are a couple of remedies tried on Marianne.

In Ch. 29, Elinor gets a glass of wine for Marianne and it makes her more comfortable. To me, this does not seem as though it would help in the case of "an aching head", "a weakened stomach" and "a general nervous faintness". But it seems obvious that this was a remedy, for Mrs. Jennings also offers the fine Constantia wine that helped her husband's cholicky gout.