Lost Earnings on SIMPLE IRA Employee Deferrals not Deposited Within 7 Business Days?

An involuntarily terminated participant is demanding her former employer make up lost earnings on more than six years of "late deposits" of employee deferrals because they were not made within 7 business days of being withheld from her pay.  The former employee is also demanding that all similarly situated participants be "made whole," as well.

At https://www.irs.gov/retirement-plans/retirement-plans-faqs-regarding-simple-ira-plans, IRS says, "You must deposit employees' salary reduction contributions to their SIMPLE IRAs within 30 days after the end of the month in which the amounts would otherwise have been payable to the employees in cash, according to IRS rules. . . The Department of Labor rule for deposit of the salary reduction contributions may be stricter. They do have a 7-business day safe harbor rule."

The SIMPLE IRA Plan Sponsor Guide from the Capital Group similarly states, "For SIMPLE IRA plans, employee contributions must be remitted as soon as they can be reasonably segregated from company assets, but in no event later than 30 days after the last day of the month the contributions were withheld. For plans with fewer than 100 participants, employee contributions deposited no later than the 7th business day following withholding by the employer will be considered timely."

All deferrals were deposited within 30 days after the end of the month in which they were withheld, though at least arguably, the amounts might readily have been contributed within 7 business days.  Is the employer at risk of liability for lost earnings on amounts not deposited within 7 business days (or such longer permissible time by which it would have been practicable to do so)?

This former employee appears determined to hold the employer "accountable" and has threatened to have the Department of Labor investigate.  Might the employer also be liable for excise taxes or other penalties if it is determined that it could reasonably have deposited amounts earlier than it did?