As long as she is still in valid L2, you can. The last action rule will kick in and the last application approved will stick.
The information contained in this answer is provided for informational purposes only, and should not be construed as legal advice on any subject matter,not should it be viewed as establishing an attorney client relationship of any kind.
COS from L-2 to F-1 and withdraw the COS L-2 to H-4. It would be in your best interest to work with a lawyer.
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