To the best of my knowledge, there is no easy way to do this. The best simple alternative is to make no further contributions to the 403(b) and start an IRA that she feeds through her checking account after making the required initial contribution. At Vanguard this is $3,000.
This makes for "lumpy" investing and she'll miss the convenience of NEVER having the money available to spend. But it will reduce her investment expenses and she'll be able to contribute $5,000 a year if she is under 50, $6,000 a year if she is 50 or older.
Scott