That is wrong. If the OP’s counselor writes about it in their letter of recommendation, that will be considered. However, the essay is NOT the place in which a student explains why they got lower grades.
Some of the issues:
A. while it’s positive that the OP’s mother’s cancer had a negative effect on their academic performance, there is no way for the college to know whether the OP’s performance would have been good enough for the college if their mother had not suffered from cancer.
However, a letter from the OP’s counselor can include something to the effect of “OP is an excellent students, and, had their mother not suffered from cancer, their GPA would have been high enough to qualify”, of something implying that.
B. Despite what everybody seems to think, the “I suffered but persevered” essay topic is not a good topic. The essay should say something about the OP’s personality, not about their history, as difficult as that history may be. AOs do not recommend to accept a student because they have sympathy for the student.
@medigeek I’m really sorry about your mother’s cancer - it’s not something you should have had to deal with. However, such an essay is problematic, if only because it usually violates the Cardinal Rule of the College Essay: Show, Don’t Tell.
Look over your essay, and think “based on this essay, do I think that the writer would do well in this college, and would be a good addition?”.