Each of you needs your own basis. If she independently has a qualifying year and specialized knowledge or managerial duties, the company can file a separate petition for her. Otherwise she may accompany you as an L-2 spouse, and as an L-2 spouse she is employment-authorized incident to status, which may make a separate petition unnecessary.
Compare a second petition with L-2 authorization
The company's instinct is often to file two L-1 petitions because both employees are valued. Test that against the facts: does the spouse have her own continuous year, and does her role at the US site require her particular knowledge or involve managing others? If she is a customer-service supervisor whose role could be filled locally, a second L-1B petition may be refused while an L-2 admission would succeed and would still allow her to work for the company or anyone else.
The L-2 route has one caution: her right to work is tied to the principal's L-1 status, so if the specialist's assignment ends or she changes status, the spouse's authorization ends with it. The separate-petition route gives independence but requires a full evidentiary case. Children under twenty-one may accompany either way in L-2 status, may study, and may not work.
Decide based on the spouse's own evidence, not on a wish to keep the family's statuses symmetrical.