@vdbfamily
The funding would come, if applicable, via the BAföG system.
There are digital options now, something which didn't exist when I was there.
https://www.bafoeg-digital.de/ams/BAFOEG
One thing which she should consider, though, is that she may find it difficult to get as much support as she might need; something else is that it could be difficult to make new friends. It's true that there are a lot of students in Heidelberg, but it's also possible to feel quite lost there.
It's also possible to find oneself speaking English quite often there; not only are there native English speakers in the town, the majority of the students and staff speak English very well and like to speak the language when they can.
If she is going to do her year abroad there, I would strongly consider staying where she is at her UK University and taking every opportunity to work on her German.
Something she could consider could be the summer school this year in Heidelberg.
She could do that during this coming summer, return to her UK Uni for her second year and then return to Heidelberg for her third academic year.
https://www.zuv.uni-heidelberg.de/international/ferienkurs/faqen.html