Your mom is correct that “Se atacó la persona ayer” is ungrammatical.¹ You need the personal a here before the direct object, just as in any other sentence where there's such a specific animate object. For the purposes of correct grammar, you need to think that the se in this passive usage can be replaced by alguien (if the verb is singular) or algunas personas (if plural). The subject slot, in other words, is occupied by se; the rest is just a normal sentence.
I find it strange that a native speaker could be “unfamiliar” with passive se in the past tense. This construction is found in all tenses and also common, even more so than the periphrastic passive (ser + participle). It's true that one mostly hears it in the present; for example, one common way to provide instructions is to use the passive se in the present, e.g. “Se coloca esta pieza aquí, luego se ajusta este tornillo, finalmente se cierra la tapa.”
The past tense passive se construction often appears in formal writing; a list of se passives often reads like a technical description, e.g. “Se extrajo sangre del paciente, la misma se testeó usando el protocolo XYZ, no se hallaron rastros del virus.” But really this is just a change in tense; the syntax and the meaning are exactly the same. What your mom might be trying to say is that using the se passive in the past is unusual in speech or informal writing, which is true. Passive voice in general is often formal anyway.
¹ Atacarse (intransitive, not passive) is slang in Argentina; it means “to get extremely worked up about something, to become hysterical”. But that's not the meaning you're trying to convey here.
