And I would say this greatly depends. If this person has been committing some flagrant fraud and they know it, perhaps an attorney might be a good idea. And it that's the case, you doubtless have enough money to pay that attorney, because you didn't need the welfare in the first place.
But you forget, these are people who are qualified or somewhere in the vicinity of qualified for public assistance. They probably don't have a lot of spare income for an attorney to represent them, and may not need one. They may want to talk to Legal Aid, but actually, even more so than unemployment insurance, "welfare" or whatever it is called in your state does audits and quality measurements and cross checks of income all the time on almost everyone who signs up.
We can't be sure from the information we have here. What this person has received may be nothing more than a "you're being called in to determine if there has been fraud in your case due to some questionable activity we have intercepted," or it may be a regular periodic check to determine if this household is filing correctly and is fully eligible for the benefits and no circumstances have changed. Or it may be that a pissed off family member or friend has called in and reported this person for welfare fraud, whether they are committing it or not. The agency will always send out a letter and do an investigation when they get a call like this, whether they actually find any fraud or not.
I have known social circles where that was standard operating procedure, when you got mad at someone, you automatically called the fraud hotline of the food stamp and public assistance programs and reported the person was committing fraud. Having this person who'd been reported go out and lawyer up and refuse to answer any inquiries until it actually went to civil court would be a very bad move in this case.
Public welfare is an agency, not the criminal court system. Because of the total likelihood of fraud going on all the time, and the constant public criticism of the system due to this fraud, they run investigations all the time. When you are investigated it's not the best idea to lawyer up and stop talking immediately. When you sign up for any needs based public assistance, you sign away your rights to privacy in most every area of your life. When you've agreed to this stuff in order to get the benefits, they don't have to have a warrant to access your tax records, your bank accounts, you dwelling place, etc. to determine if you qualify for assistance.
Refusing to cooperate with this investigation will do nothing but get them to up the ante, probably cause you to be the one who is prosecuted civilly instead of just the standard things, like being sanctioned, and unable to receive benefits for a few months. Legal services for the low income in your area will be a very good resource for you. Most of them have lots of material which will explain to you exactly what the welfare office can and can't do in terms of "investigating" you for welfare fraud and how to reasonably protect yourself from being unjustly sanctioned.