You should contact the surrogate's office at the courthouse in the county in which your mother-in-law resided. Explain that she had no will and only one bank account with a small balance. If you have her death certificate, they will help you obtain a short certificate. The clerk in the surrogate's office can tell you what you need to do, give you the correct forms and tell you who needs to sign them. Once you obtain the certificate, work with her bank to obtain the funds in the account, pay her bills and return funds to her pension fund. You can probably do this without a lawyer, and without taking days off from work (though I believe you will need to visit the surrogate's office at least once).
Disclaimer: This is answer is offered for general information and not legal advice or to establish an attorney-client relationship.