Besides the consequences that a US citizen would face if convicted of a crime involving domestic violence, your mother has additional problems involving her immigration status.
In general, persons who are not US citizen and are convicted of a crime involving domestic violence are deportable from the US. Besides being deported, your mother may face a lifetime ban on being admitted into the US for any reason.
So, your mother likely does need an attorney to advise and represent her. She may qualify for a public defender. She can also hire a private attorney.
In short, the answer is yes, your mom should probably get an attorney. As Mr. Nguyen pointed out she is facing not just potential criminal charges but immigration issues as well. I don't know if she plans to remain in the US and, if so, how often she plans to return to visit, but a DV conviction can have huge consequences on these rights. Hopefully she will be released at first appearance but there may be a no contact order between her and your wife which will mean that she will need to find another place to stay right now. She's also going to want to resolve this case before she returns to India or a warrant may issue for her arrest meaning she may be arrested upon entering the country the next time she comes for a visit.