A previous answer says that 3 female characters are mentioned in The Hobbit:
- Belladonna, Bilbo's mother
- The mother and Fili and Kili
- The wife of Girion of Dale
I can add :
- 2 sisters of Belladonna, as it is mentioned that she is one of three of the Old Took's daughters
- Gollum's grandmother. In the chapter Riddles in the Dark, "Gollum brought up memories of ages and ages and ages before, when he lived with his grandmother in a hole in a bank by a river"; and later, "Gollum remembered thieving from nests long ago, and sitting under the river bank teaching his grandmother, teaching his grandmother to suck - "Eggses!" he hissed."
There are also females referred to, in the plural:
- First chapter. We know that there are hobbit girls as well as boys "[Gandalf] had been away over The Hill and across The Water on business of his own since they were all small hobbit-boys and hobbit-girls."
- Smaug is said to devour inhabitants of Dale, especially young women. "Later he used to crawl out of the great gate and come by night to Dale, and carry away people, especially maidens, to eat, until Dale was ruined"
- Finally, when inhabitants of the city of the lake flee from the fire, "women and children" get into the boats.
So, though there are no female roles, we at least get to know that hobbits and men have daughters and wives. As for elves, there is no mention of females ever; and for dwarves, the sole mention of the mother of Fili and Kili is very short. Yet, it doesn't say that there aren't females elves and dwarves, it's just that they aren't specifically mentioned.
Quite often, we think that there are female characters in the hobbit, because they are in The Lord of the Rings, like female elves, female hobbits, and we mix the two stories in our memory. But in The Hobbit the terms stay in the gender-undetermined plural : the elves, the hobbits, the Sackville-Bagginses. As an example, in the last chapter, the Sackville-Bagginses are suspected of stealing the silver spoons but it's "they". No mention of Lobelia in The Hobbit; she appears only in The Lord of the Rings.
