She can have multiple, concurrent H-1Bs, so long as there are no issues with regard to the H-1B cap. Each H-1B employer would need to file a separate H-1B visa petition on her behalf before she could start working for them.
If I read your question correctly, your spouse remains in H-4 status at present and has a prospective H-1B petition in process with one attorney, and a second job offer for which there is already an H-1B approval, but not a change of status.
If the petition for the first job is filed already, you don't really have any choice about working with that lawyer, other than to abandon the job offer; if this is prospective, for an April 2009 filing, you can contact the employer and ask if it is OK to move forward with another lawyer, but you will have to pay the first lawyer for any work done to date. If your wife just wants to change status to H-1B as soon as possible based on the second H-1B approval, then employer#2 (through lawyer#2) can file an amended petition, requesting a change of status...if you are currently employed and maintaining valid H-1B status, and she can thus provide current proof that she is maintaining valid H-4 status.