Mrs. Honour is Sophia's maid, and her ability to mingle with servants and catch up on gossip ends up being useful to her employer: for example, it's Mrs. Honour who first hears that Tom is staying at the inn at Upton. But beyond Mrs. Honour's role as a plot device, she does not have much depth as a character. Partridge is a much more complex and (if we may say) realistic character than Mrs. Honour.
Mrs. Honour is a huge chatterbox. She just goes on and on and on. Her dialogue appears as these huge, intimidating blocks in the novel—we have to wonder when she has the time to draw breath. Of course, her talking is mostly gossip about the other characters: not only is Mrs. Honour the one to first reveal Tom's love to Sophia, but she also seems to know that Lady Bellaston keeps a love nest in another neighborhood from her actual house. Mrs. Honour knows a great deal, but you have to sift through a lot of extra information and random commentary to get to any substance.
Besides being a giant gossip, Mrs. Honour is also a huge snob. Her physical fight with Lady Western's maid and her offensive behavior towards the other servants in the inn at Upton both come from her desire to prove that she is a better class of servant. Since her own social position is pretty weak, she wants to make the best of it by pushing down those who are even lower down than she is.
Also, Mrs. Honour's loyalty is available to the highest bidder. When Sophia first proposes her plan to travel to London, Mrs. Honour decides to sell out Sophia to Squire Western for a big reward. The only reason she doesn't wind up doing this is because she gets fired for fighting with Mrs. Western's maid before she can tattle on Sophia. Once Squire Western has dismissed her, Mrs. Honour has to go with Sophia to make any money at all. And Mrs. Honour will do pretty much anything for a buck.
These three traits—gossip, snobbishness, and money-grubbing—actually seem to be common to all the maid characters in the novel. Lady Bellaston's maid Mrs. Etoff is the one who first tells her how handsome Tom Jones is. Mrs. Etoff must be pretty in the know, to be aware of Tom's appearance when he's been in town for, like, two days.
Mrs. Western's maid is so snotty about her position as a London-dwelling servant that she provokes Mrs. Honour to pull her hair and scratch at her—now that's intense snobbery, the kind with punches behind it. And the maid Betty sells out Sophia to Mrs. Western by telling her boss that Sophia has been receiving letters from Tom Jones. Betty does this for a financial reward. Clearly, Fielding believes all maids are greedy, gossipy snobs—these traits appear to go along with the profession rather than the individual.