Upvote:4
Your application will be much stronger now that you are enrolled in a PhD.
That is assuming that you also have a visa that will allow you to stay in Germany for the duration of the PhD, or at least for several years of it. Being enrolled in a course of study gives you much stronger motivation to return to Germany after your visit to the UK.
However the rejection letter also points to you not having provided enough information about your financial situation. You need to provide bank statements and other documents to indicate what your expenses are, and how you pay for them. Primarily it's not about "do you have enough money to pay for the visit to the UK", but "Do you have enough money coming in, relative to your expenses, that paying for a visit to the UK makes financial sense?" Does your scholarship pay all your expenses? Are you doing a job in addition to your studies? Are you paying your expenses out of savings?
The letter from your partner's family stating that they will pay your expenses while in the UK will be helpful. A letter from the hospital will not be a lot of help - your partner being in hospital will not be a big factor in the decision. Anything that backs up your claim of being a student will help somewhat.