Final answer:
The sentence is correct and requires no changes. It is important to proofread carefully, as spell check may not catch all errors, especially those involving correct word usage.
Step-by-step explanation:
The sentence provided is correct, and there are no incorrectly used words: "Before she had access to the Internet, Mrs. Li often wrote letters on personalized stationery." As part of the proofreading process, it's vital to spell check your work, read it thoroughly to catch any errors that spell check may have missed, and ensure that you have used the correct words in the context. For instance, making sure that 'there' is not used in place of 'their'. After a thorough review for correct grammar, spelling, and punctuation, one should also ensure that the document adheres to any necessary formatting standards, such as MLA or APA guidelines.