Her expertise is relationships and there she is fighting with others, breaking up fights, name-calling, and taking credit for the fact that her ex-husband's wife is a normal, decent, likeable person.
The reason the three get along isn't because Siggy made her that way and put her relationship expert skills to work.
Obviously the producers felt none of that produced any episode-worthy footage. I realize it was from pneumonia that can be deadly but all the endless stress and embarrassment they caused her must have broken her heart and weakened her immune system because a lot of stress over a long period of time will surely do that. And then her daughter ends up all over the news for lying to the banks, cheating and embezzlement and ends up in jail so she has a criminal jail-bird daughter in prison for a year, which is very hard on a parent. Then she sees her grandchildren, whom she adored, suffer through all that, plus the imprisonment of her son-in-law.
Teresa's storyline seems to be only about dealing with her mother's death and looking after her family while her husband is in jail. She watched as they cried over their dad going away even though he's a douche.
Like any loving grandmother she felt great sorrow for the kids all along.