When I first read this myself, I found that I did not like Mrs. Jennings either. She reminded me a bit too strongly of Mrs. Bennet in P&P, who I absolutely hated as an ignorant social satire. However, after becoming more accustomed to the character of Mrs. Jennings, I found her to be almost heartwarming. She has no idea that her "thoughts" are crash, improper, and cause offense to people of taste. I cant dislike a character who I pity for being naive and friendly, with the misfortune of being overly so.
She may not be the type of person who you could stand to have an actual aquaintance with, but she has her good side, which I feel entitles her to a bit of leverage. In short, she is fun to read, and appalling to meet. She does seem to be a striking social satire, but one that I can warm up to, which makes her all the more interesting, and all the more complex (confusingly so).