I cannot see anything particularly admirable about Mrs. Mooney. It seems to me that James Joyce wanted to portray her as a vulgar woman who used her naive daughter to entrap Bob Doran into marriage. The family is depicted as being socially inferior to Doran. Polly's father is described as "a shabby stopped little drunkard." Her brother has a "bulldog face." Doran is afraid of him. Here is now James Joyce describes Polly's brother:
Jack Mooney, the Madam's son, who was clerk to a commission agent in Fleet Street, had the reputation of being a hard case. He was fond of using soldiers' obscenities; usually he came home in the small hours. When he met his friends he had always a good one to tell them [i.e. a dirty joke] and he was always sure to be on to a good thing--that is to say, a likely horse or a likely artiste. He was also handy with the mitts and sang comic songs.
This is quite a family that Doran will be marrying into. Mrs. Mooney and Polly have an unspoken understanding that it is all right for Polly to sleep with Doran. The mother wants to get him involved so deeply with the girl that he will have to marry her. The idea here is that he has ruined her marital prospects by depriving her of her virginity and must do the right thing by her.
She knew he had a good screw for one thing and she suspected he had a bit of stuff put by.
The phrases "good screw" and "a bit of stuff" are Joyce's interpretation of Mrs. Mooney's thinking. She wants to get her daughter married off, and Doran is the most likely prospect because he is a gentleman with a good job and some money saved.
The only thing "admirable" about Mrs. Mooney is that she is able to support herself and her two children without the help of a husband.
Mrs. Mooney was a butcher's daughter....She dealt with mooral problems as a cleaver deals with meat...
Jig, in "Hills Like White Elephants," is a great deal more like Polly than like Mrs. Mooney, but Jig is obviously more intelligent, better educated, and more sophisticated. Furthermore, Jig is pregnant. It appears that Polly is not pregnant, although she has been intimate with Doran for some time. Jig is not religious. She and the man have no apparent religious qualms about having an abortion. Jig travels freely around Europe with a man--something Polly would never dream of doing in Catholic Ireland. There is good reason, in my opinion, to believe that Jig and the American may already be married. He just doesn't want to get burdened with a baby; whereas Bob Doran doesn't even want to get burdened with a wife and senses he would be marrying into a deplorable family, with a good-for-nothing father-in-law, a domineering mother-in-law, a brother-in-law whose interests are confined to drinking, brawling, and gambling, and a wife who may seem sweet now but could become like her mother. Polly is simple-minded, uneducated, and common. Doran, who is sensitive and intelligent, is being set up and trapped by a shrewd, vulgar, low-class woman. The men who live in her boarding house refer to her as "The Madam." This is the way men customarily refer to a woman who runs a bordello. Mrs. Mooney could serve in that capacity very efficiently.
Polly knew that she was being watched, but still her mother's persistent silence could not be misunderstood. There had been no open complicity between mother and daughter, no open understanding but, though people in the house began to talk of the affair, still Mrs. Mooney did not intervene.