You should consult first with the counsel of record for your L1-B who presumably would handle the L1-A as well on behalf of your employer. Good luck.
The answer above is general in nature and provided for informational purposes only. Specific and reliable answers will require a better understanding of all the facts and information about your case. You should consult with an attorney who can analyze the facts and law specific to your particular situation. Please be advised that the answer does not constitute legal advice and may not be viewed as establishing an attorney-client relationship of any kind.
It depends in part on whether you would be taking on a new position that qualifies for L-1A classification, or if your current L-1B position dual-qualifies as an L-1A position. Your employer's immigration attorney should be able to provide guidance in this regard. All else being equal, your wife's L-2Spouse EAD will continue to be valid as long as she holds valid L-2 nonimmigrant status.
In general if the job qualifies for L-1A and you meet those qualifications you can switch from L-1B to L-1A. If the transfer is successful your wife can maintain her employment authorization. You should speak to your employer's lawyer who knows your specific work situation and discuss your concerns and possible risks with him/her.
This answer is provided solely for informational purposes only. You should always speak directly with a lawyer. This answer does not constitute legal advice or create an attorney-client relationship.