Translation:No, mom did not go to the store yet.
Shouldn't it be "пошла" instead of "ходила"? I thaugght "ходила" was imprerfective/habitual so it implies something like "No, mum hasn't BEEN GOING to the store". "Mum hasn't been/"gone" to the store" should be more like "мама ещё не пошла в магазин", shouldn't it?
«Пошла́» implies a single one-way trip, and mum is not expected to stay in the store too long: she'd buy something and return, so that's why «ходи́ла» is used.
For one-way trips, «пошла́» would sound OK: «ма́ма ещё не пошла́ на рабо́ту» (because she's expected to stay there for some time).
The same is true for other verbs of motion. «Ве́ра ещё не пое́хала во Львов» implies that Vera will spend some time in Lviv, while «Ве́ра ещё не е́здила во Львов» implies Vera wants to visit Lviv for a short period of time and return.