If Margaret died earlier then?
Possible but not likely. Elizabeth had done an excellent job at making the Protestants hegemonic economically, politicaly and militarily very quickly at the beguning of her reign. They will form a rather formidable opposition to Marry. A great political mind would probably be needed to handle them and Mary Stuard didn't have that, in fact she wasn't able to handle a rather similar situation in Scotland.Elizabeth becoming fatally ill earlier than she died otl might be a option?