shad0w, a couple of points.
(1) Not everyone has the opportunity to attend a full-time class. Although in this case, Teresa is doing to do a homestay, so presumably she's a student. She has less excuse unless she lives in a small area without much opportunity to practice the language (community college, etc.).
(2) It is absolutely impossible to be fluent in a second language after three years of study unless (a) you are a genius/savant, or (b) you are in the country of the foreign language.
Even after living in Japan for a year, studying for three in a university setting, including getting a degree in the language (in addition to another, to be fair), and continuing my usage for the past three years since graduation, I still wouldn't consider myself to be fluent.
Fluency is very, very difficult to achieve. It takes years and years. Hell, it takes years and years of living in the country in which the language is spoken natively.
It is very possible, with hard work, to be conversational after three years. But fluent? Highly unlikely.
In my honest evaluation, I'd say Teresa is where I was after a year. However, I was attending a group of native Japanese speakers to practice with them, and I have a natural gift with languages. I wouldn't be too quick to judge her work ethic.
I think her composition skill is decent for an off-and-on three-year student of the language.
And there's no way anyone who has ever attempted a language other than Japanese will say it's an easy language. Aside from the ridiculously complex writing system compared to 95% of the other languages out there, anyone who is coming from an Indo-European language system is in for a shock, as word order and so many culturally-affected grammar points are extremely different. Just for one example, auxiliary verbs in Japanese become part of the verbs themselves, while in English, Spanish, etc., they are still separable:
Yo
he comido.
I
have eaten.
食べ
ます。Yes, "-masu" is an auxiliary verb!
Origin of -masu There's an excellent discussion about where it comes from (by a knowledgeable native speaker), if you care to broaden your knowledge of Japanese language history.
Japanese is considered by many US government organizations who have studied language acquisition (CIA, State Department, etc.) in order to effectively instruct their employees to be one of the hardest languages for a native English speaker to learn.
In case anyone's curious, if I recall correctly, Dutch was considered one of the group of easiest languages to learn. I think it was classified as easier even than German, Spanish, etc.
I speak Spanish, English, and Japanese, can read French, Italian, Portuguese, and have some small ability in Chinese. The only language harder than Japanese in that list is Chinese, in my opinion.
And the only reason I say Chinese is harder is because of the writing system. Despite "seven" years of study in Japanese, compared to a semester of Chinese, my Chinese accent is closer to native. Furthermore, the sentence order is very much similar to English. It's just those darn hanzi!