First hi there and welcome to YT
A one year guarantee is extended by most reputable breeders. Perhaps you can talk with her and ask why she doesnt extend the guarantee, if she doesnt give good sounds reasons, I would not consider purchasing from her. Make sure her guarantee covers LP's and Liver shunt, these things usually will show up within the first year if they are in the dam/sire genetics.
read California lemon puppy law it states the breeder is obligated to pay for any congenital or hereditary defects for 1 year.
http://www.malteseonly.com/lemon.html
hope this helps