You could always buy it from them privately and rent it back to her with an option for her to purchase it after a set period of time. In that scenario you would have to be prepared to lose the friendship... Its an investment if things do not go as planned out you'd need to evict her to protect the asset. You could also purchase it together you be the money partner and them being the managing partner but you already have default concerns on your mind so in this situation I would want full control of the asset in case of the worst. So maybe a compromise would be you buy it yourself and pay her to manage it, in her rent contract there could be a purchase option. She would make some additional income a percentage of the rent that could be put back towards a down payment for the later purchase. You should also seek some concession for the work needed, I'm not familiar with your market but I would assume other offers would have repairs requested. Protect yourself first you want everything in writing and when you work with friends and family be prepared for the relationship to suffer if things go poorly.
