Florence Gibbs is a non-canonical character created for the 2009 ITV adaptation of Murder is Easy. Florence, also known as "Florrie" was the grandmother of Amy Gibbs. The opening scene in the episode showed a church service in which the curate Henry Wake asks the congregation to remember the recent passing of Florence. She had apparently died after putting poisonous mushrooms into her stew. Florence Gibbs is mentioned only and does not appear on screen. In the original novel, Amy Gibbs has an aunt Mrs Church but this is not a parallel character and has a different plot role.
According to various village accounts, Florence was considered a sort of village witch. She lived in a "crooked little cottage and all those lotions and potions" and was "very good with warts". She was regarded as a "real country woman". Therefore Miss Marple considered it inexplicable that she should put the wrong kind of mushrooms (which were poisonous) into her stew. Another clue was Amy Gibb's mention that her grandmother "and Uncle Henry" often helped people. Discovering who Uncle Henry was became another line of inquiry.
It is only towards the end of the episode that Florence's relevance to the plot is revealed. The reference is horticultural. Amy had marked it on a book (probably "Nature's Poisons" which had been stolen from the library). Miss Marple discovered that "Old Uncle Henry" is another name for the herb Mugwort. When combined with "Tanacetum vulgare" or "Pennyroyal" the resulting potion can be used to induce abortion. Florence had been dispensing this potion and she had been murdered to preserve the secret that someone in the past had wanted an abortion.