You are right to be cautious in this situation. Your daughter and her fiance need to understand the entire situation before purchasing this house. Your daughter's agent should fully explain what is meant by "a chance there is a lien." That agent is obliged to put your daughter's interests above his own as he counsels her through a home purchase.
A lien is a claim against property that must be repaid. For example, when someone takes out a mortgage on a house, that creates a lien against the property. If someone takes out a second mortgage, such as a home improvement loan, that also creates another lien against the property. In this example, there would be two liens on the house. When this house is sold in a normal manner (not a Foreclosure or Short Sale), both liens must be repaid by the Seller.
In a Short Sale, the lender or lien holder agrees to take less than the full lien amount owed by the Seller and allows the house to be sold. In the example above of someone having two liens, the lender of the first mortgage may agree to the Short Sale. However, the lender of the second mortgage may refuse and prevent the Short Sale. A result of this refusal may be that the house goes into Foreclosure. Then, neither of the liens is paid, and both lenders lose.
There are other reasons liens that are recorded against property; i.e., if the taxes were not paid, If a repairman fixed the roof and was not paid, if the Seller had a judgment, etc.
When you say Quick Sale, do you possibly mean Short Sale? If so, your daughter may be encountering a lien holder asking that the Buyer (your daughter) pay off the lien owed by the Seller. If the house is a real bargain, a Buyer may want to consider to consider it. Otherwise, there are many other great houses available.
Best of luck to you and your daughter,