Last December, I loaned my mother money to purchase a co-op share in Florida. We put the share in her name. My mother has recently taken sick and will need nursing home care. At the time of the loan, we did a 7% note from her payable to me and had it notorized at a bank. According to the agreement, the loan is payable at the time the co-op share is sold. Do I need to record a lien somewhere to protect my interest? My concern, is that since the share is entirely in her name, that it will be considered as part of her estate and all of the proceeds will be required to be used for her nursing home care. She otherwise has very limited assets.

Yes the note should have been done as a mortgage and a lien filed against the co-op shares. When purchasing a co-op you aren't actually purchasing property. You purchase shares in a corporation. Those shares entitle you to use of the co-op unit while you own those shares. Unless you have your interest in the shares recorded, then the whole value of the co-op will be considered part of her assets.

Is it too late to record my share. If not, how do I go about doing that?

It probably isn't too late. I would contact the co-op board about how to do it.