In Beverly Cleary's Dear Mr. Henshaw, we learn Leigh's mother is a very hard worker with a lot of integrity, which means she is very dedicated to doing what's right.
We know Leigh's mother is a hard worker because, in the letter dated November 23rd, Leigh tells Mr. Henshaw that his "mom works part time for Catering by Katy," a catering business his mother's friend runs. His mother has known Katy since they were kids. His mom only works part time because she also takes a "couple of courses at the community college" to become a Licensed Vocational Nurse (LVN); Leigh explains LVNs work as assistants to "real nurses." His mother takes these courses to provide a better life for her son and herself, wanting to be able to afford more than a mobile home or a small cottage that is "sort of falling apart" ("November 24"). One reason she divorced her husband is because she felt he was not using his money wisely enough to get his family out of the mobile home; she thought he wasted money by buying his own 10-wheel truck for cross-country work when the money could have been put towards his family and home.
We know his mother has integrity because, when she finds the letter in which Mr. Henshaw took the time to write Leigh a list of questions in order to get to know Leigh better, she insists Leigh answer the questions he had decided to ignore because he was mad Mr. Henshaw took so long to answer Leigh's own questions to Mr. Henshaw. Leigh's mother tells Leigh to answer the questions because she thinks "if [Mr. Henshaw] took time to answer [Leigh's] questions, [then Leigh] should answer [Mr. Henshaw's]" ("November 16"). In other words, Leigh's mother sees how important it is to give to others just as much as others give to us.