Translation:My grandmother used to pray at the church every morning.
most times you need a 'determiner' before french nouns. Articles are determiners. Some prepositions like 'en' /sans are determiners. Quantitative phrases/words are determiners... like vingt (twenty apples) beaucoup de pommes (a lot of apples). But prepositions of position/place like 'a' and dans' and 'a cote de' etc need the determiner (USUALLY one of the articles) before the noun which follows. I think you are being thrown by having to translate phrases like "we are at church" in english to literally 'we are AT THE church' in french. But remember you can say "i eat apples' in english but MUST say literally 'i eat (some/the/two/...essentially a determminer) apples in FRENCH!