No, no, NO!!! Paying the bill will NOT automatically make you the owner. Your friend received a Notice of Trustee's Sale because SHE is the owner and has all rights of ownership. Consult an attorney if you wish you to obtain ownership or an equitable interest in the property which your friend must agree to give. An attorney can also help ensure repayment of your funds by promissory note and deed of trust she you decide you simply want your money back.
Yes, the days are dwindling and the knee-jerk reaction is to step in and help. You should. But you need a plan to "keep the business as business" so you can maintain your friendship.
Again, you need an attorney. There is much more to the story than I have written.
Good luck to both of you!!