Recently my wife's check was garnished over a debt that was from 2005. What can we do about it when the collecting agency said they couldn't sue over the debt due to law limitations but a new law firm filed suit against her
This may be somewhat confusing to you, but the fact that a statute of limitations has run on the debt doesn't make the debt go away. What those statutes do is to supposedly deprive the creditor of the right to use the courts to enforce the debt if it is outlawed by the statute.
The confusing part is that most, if not all state hold that the running of a period of limitations is an affirmative defense. A critical phrase, which means that it must be pleaded in response to an action on a debt that the law says the creditor cannot file upon. (?)
And if the debtor/defendant fails to plead the statute in defense to the claim, that is, file a written answer to the claim asserting the defense of an applicable statute of limitation having expired, the protection seemingly afforded to the debtor is deemed waived - gone, kaput!
So, if someone is sued on a debt they think is outlawed by a statute and they do nothing believing that they don't have to do anything, they often get stuck with a default judgment from which there is no right of appeal.
Certain remarks in your post suggests to me that you didn't first learn of the lawsuit when the garnishment hit your wife's employer. But go to the offices of the clerk of the court where the case originates, ask for and read the court file. After which you may have other questions.