I'm in the Netherlands, the basics of housing, petrol, cars, groceries, health care, taxes, etc. are high. The housing market is always crazy, but with better economic times (as they are now) it goes insane. Single parents have it hard despite there being quite a lot of supportive measures/services, I know many who have coupled up a lot quicker in part as a financial incentive. Salaries are higher than in Germany but I'd posit you'd have more spare income left there.
If you're in education there is a shortage of teachers (not sure on assistants) so if you were willing/able to retrain into a teacher there are a lot of schemes to incentivise that. I believe the salary for teaching assistants isn't very high, and it wouldn't leave you much as a single parent once all the bills are paid. Housing will take up the bulk of costs and in the large cities you won't have access to social housing for quite some time due to long waiting lists.
Realistically, getting employed as an English speaker will only happen within the Randstad area. The Hague is particularly expat friendly, so is Amsterdam but it's more expensive and the majority of international institutions are in The Hague. If you can get a job with one of the international institutions you'd be doing very well as they do not have to pay any taxes on that income but it also means you have no access to social benefits should you find yourself in need of it. There are also several English language schools you could apply to (the British School, the American School and the International School) and they usually offer a staff rate for their own children to attend. However, especially in The Hague, there are several secondary schools that offer bilingual education, TTO (Tweetalig onderwijs) where students with an English speaking background get preference in selection.
I would point out that secondary education starts in year 8 here and it's tiered into potential further education (vocational-college-university). Year 7 is pretty much geared around prepping for a standardized test that indicates capability, I'm not sure what the process is if you're coming in from abroad, but I would point out that it could be quite frustrating that she's placed in a lower tier than capable, and thus limiting her choices in further education on account of language. You can move up sometimes but you'd be losing a lot of years in the process.
Are you an EU national outside of the UK though? I think potential employers will show some hesitance WRT UK employees so long as Brexit has not been fully negotiated.