The question is, and therefore it would not matter who owned the store (and it really bugs me when people emphasize “frum-owned” as if non0frum and non-Jewish people are hefker), did she make a kinyan by putting them in her cart. If she did then it might be theft (although presumably, someone else would then buy them so in the end there was no loss). If not, it is analogous to giving someone a lift and thus saving the person the cost of public transportation.
