汝、聖母マリア様（or the name of the object person)を大いに愛せよ！
あなたの世話をします might mean something else.
This means she takes care of you, for example, feeding you when you cannot eat yourself, supporting you when you cannot walk by yourself, changing diapers of you when you cannot do elimination by yourself.
If you use 彼女, the context may mean a completely different thing:
"Love your girlfriend a lot, pray a lot for your girlfriend, then she will take care of you, such as changing your diapers."
(I think it is far from religious context, right?)
Okay, anyway, if you don't want to specify the name of the woman, I would suggest: 汝、あの方を大いに愛せよ！ 汝、あの方に多くの祈りを捧げよ！ （さすれば）あの方は汝を救ってくれるであろう！