I would pass on the 99's. I use them, but land all of my doubles and am working back on triples again. They are really meant for a higher level skating, and I know from currently using them that they might cause some issues for your daughter. One of the main reasons is the rocker. The beginner blades have a rocker designed for beginner jumps, spins, etc. The 99's are for skaters doing advanced jumps and spins, and is really meant for better control on those type of manuevers. Although she would get used to using the blades, I think she'd benefit from the lower-level blades that are designed for her skating skills.
Also, a good point was made that they are cheap at this moment because you were lucky enought to find a used pair, but if they aren't really needed at this point, then you will end up with a much more expensive bill for new equipment down the road. I think most places retail 99's for around $450.
Hope that helps in your decision process.