I'm Lucy, and I'd be happy to answer your questions today. I'm sorry to hear that this happened.
That clause in the lease is void. Any language in a lease that purports to waive the tenant's protections under the Landlord Tenant Act of Virginia is unenforceable as a violation of public policy. Code of Virginia, Section 55-248.9. Because she put a void provision in the lease, if you had to sue her, you'd be entitled to collect your reasonable attorney's from her (unless you're renting a single family home from a private party who doesn't own more than 2 rental properties).
Also note that even if the clause WERE enforceable, all it says is that she doesn't have to send you an accounting for the deposit. That doesn't say she gets to keep as much of the deposit as she wants if you didn't provide a forwarding address. She's still only allowed to keep the amounts necessary to reimburse her for unpaid rent or damage to the property. If you did not owe rent when you left and the property was in good condition, you can sue for the 30% she withheld.
You have two options here:
1. Send her a letter explaining that the provision she's relying on is void and pointing out that, if you sue her, she still has to justify the deductions to the judge. It's actually in her best interests to tell you why she's keeping the money if her reasons were valid.
2. File a suit in Small Claims Court to recover the amounts she withheld.
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