Mrs. Joe only wants Pip to get a minimum education so he can better himself, and improve her reputation in doing it.
Pip is an orphan who lives with his sister and her husband in the marshes near Rochester in Kent, England. His uncle is a blacksmith and illiterate, and Pip is similarly uneducated. They do not have schools, so it is not usual for Pip to not know how to read and write.
AT THE TIME when I stood in the churchyard, reading the family tombstones, I had just enough learning to be able to spell them out. (ch 7, p. 31)
Pip is given over to Mr. Wopsle’s great aunt, who is “a ridiculous old woman of limited means and unlimited infirmity” (p. 31). Pip’s aunt pays her two cents a week to sleep while the boys of the village attend school, when she is supposed to be teaching them. The only person with any teaching skills is Biddy, Mr. Wopsle's great-aunt's granddaughter. Biddy is the one who teaches Pip to read.
Other than improving her standing in the community, Mrs. Joe is not interested in Pip getting an education.
“And she ain't over partial to having scholars on the premises,” Joe continued, “and in partickler would not be over partial to my being a scholar, for fear as I might rise. Like a sort of rebel, don't you see?” (ch 7, p. 34)
When Pip receives his “great expectations” his sister is more interested in the wealth than the education that comes with being a gentleman. When Pip elevates himself, he elevates her. As his education and wealth improves, her standing in the village improves.
Mrs. Joe seems to have no interest in preparing for Pip’s future other than to succumb to the fact that he will be a blacksmith and provide him the minimum socially-proper level of education. She is interested only in herself, and as a result Pip can barely read and write before he goes off to tutoring in London.
Although Magwitch seems more interested in giving Pip an education than his own sister and former guardian, his motives are not completely altruistic. His goal is to prove that anyone can become a gentleman with the right resources, and fortunately for Pip he is the beneficiary of the experiment. Therefore after he loses the fortune he has enough knowledge to get a real job and support himself.