Where do you live? There's a Finnish School for kids in Sydney. The people are lovely and she'd not be the least fluent in the group.
http://sydney.finnish-schools.org/in-en ... ontact-us/
It probably won't really matter if she goes backwards in class grade a little, she will have enough to concentrate on, even if the maths lessons are too easy in the beginning. My two went backwards a year and a half (arrived ages 12 and 13). I absolutely cannot recommend the integration classes. Half-way through the year they were still unable to say even basic greetings, they did nothing in the way of homework, and some of their classmates unfortunately spoke English, so guess what they all spoke... they didn't improve much until the following year when they went into 7th and 8th grades respectively with just Finnish as the environment. The only kids benefiting in the integration class seemed to be the Somalian kids, who couldn't speak English and who had a proper opportunity to be immersed.
So I think others are right recommending your daughter just "dive in" with ordinary classes and trust the school to support her language learning as they see fit. Try to encourage Finnish interaction... it might involve some arranged play dates with Finnish-speaking kids etc.
As for the two hours of entitled teaching... originally my two were just shoved into the 6th graders' basic English lessons. Totally unsuitable and they were bored out of their brains watching kids learn how to spell words they'd been writing when they were five. When I got a little annoyed at it being inappropriate, the integration "teacher" just shrugged, said the timetable worked that way, and really didn't care. It was only when chatting to the school counsellor that I casually mentioned it - he was shocked and gave me the info - there was an organised group at another school one afternoon per week. We sent them there faithfully for about a year despite their protestations that it was also boring

I eventually pushed to find out what was so boring and why they disliked it so much. Turns out it was essentially two hours of babysitting where the teacher/babysitters sort of used English. It was crosswords, colouring-in, watching English-language kids' shows and playing English-language board games. Granted, these are all fine as teaching methods in a social sort of environment, but my kids reckoned that more than half of the children could barely speak any English and it became apparent we were wasting our time, so we stopped bothering to go.
Your daughter's spoken English will not suffer while you're using it at home every day. Just foster a love of reading and writing, and it will keep her skills up until her Finnish classmates reach advanced English levels.