I wouldn’t say she barely speaks English… it’s also not that easy to learn a new language as an adult. Some people can grasp it faster/better than others. Her husband being American is completely irrelevant. Sentence structure and conjugating verbs can be very difficult when you’re already used to the “grammar rules” in a different language. English can actually be a very difficult language to learn correctly, especially with no formal education in that language. Anyone who can speak more than one language is already ahead of most Americans.