Since her unearned income is less than $1,300 and her earned income is less than $14,600 she is not required to file a tax return.
The IRS website you posted has a table for Dependent Income - https://www.irs.gov/individuals/check-if-you-need-to-file-a-tax-return
If federal income taxes were withheld from her wages as a W-2 employee she should file to get a tax refund. If the $4,000 was not from wages as W-2 employee but from self-employment she is required to file since her self-employment income is $400 or more. If this is the case then she needs to use a Schedule C for the income and expenses.
If for any reason she files a tax return make sure that she indicates on her tax return that she can be claimed as a dependent.
