I-129s till 30 sep 2011, I-797A says petition valid indefinitely, visa L1B stamped till 30 sep 2011, I94 valid till 2014.

This L-1 is a blanket petition - what has been approved indefinitely is the employer's representations about the intra-company relationships. The I-94 to 2014 controls your status, so you are validly in the US as an L-1 until then - the visa stamp expiration is only relevant if you travel abroad, in which case you will need a new stamp to return. Your wife can apply directly at the consulate for the L-2 with evidence of your L-1 status (your I-94, copy of the I-797, recent letter from your employer confirming ongoing employment and some recent pay statements), as well as proof of your marriage (marriage certificate). No separate USCIS petition for the L-2 would be required first unless she were here in some other status and was changing to L-2 status here in the U.S. Speak with an attorney for guidance on the process - she does need to follow the standard non-immigrant visa application process at the consulate.