I'm confused about when one should use "att" with the infinitive verbs and when one should not. Why is this, for example, not "Hon vill absolut att gå"?
You don't use att with modals. That basic rule covers almost everything. :)
Sure, but remember we're not necessarily trying for the most idiomatic solution, since the purpose is to teach Swedish words and constructions. We do accept "definitely", as well as "certainly", but it serves the purposes of the course better to use "absolutely" as the main translation.
That's odd - but likely, yes. The mobile apps have some bugs which we as course contributors can't affect at all.
What would you say for "she will absolutely go" or in other words "she will absolutely be there"
That's a different topic in itself, really. Here is a great resource: http://www.thelocal.se/blogs/swedishteacher/2014/10/01/future-tense-ska-or-kommer-att/