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It sounds like potential guards have to have combat experience or significant police experience. So it’s probably not something the average person is going to be able to do.
OTOH, a single bodyguard mercing their protectee would nuke the whole company, which would be pretty funny.
I would suggest not charging her to live there, as you own the place; that might feel excessively transactional. Perhaps what would be most reasonable is to split bills proportionally after you’ve paid your mortgage. If, for example, your mortgage alone was 2000 Euro, you earned 6000 Euro a month, and she earned 4700 Euro a month, you would say that your income was 4000 Euro to her 4700 Euro, and that the split should be about 46% (your share) to 54% (her share).