I'd also assume that by then the rules will have changed? Obviously depending on what happens during the summer, but yeah - assuming a decent chunk of people in both Germany and the UK will be vaccinated by then, the rules are likely to become more lax and more people will be able to travelSince the new academic year will start in the end of August/September, she'll probably be vaccinated by then (even if the vaccination program gets a slight delay).
If she's fully vaccinated, I think Germany will allow her to enter the country without any big problems. And even if Jade has to quarantine, she'll probably be willing to do that just like entering South-Korea
(https://www.bbc.com/news/uk-57209444)