You really need to research lead poisoning and prevention. This is very serious and can cause permanent damage. I thought I even read somewhere that any result over a 10 required hospitalization.
Young kids crawl around and pick things up off the floor and put them in their mouths, thus exposing themselves to lead dust much more so than adults. In you live in an old house, painting all the surfaces that have old paint will seal in the old lead paint, and is the easiest way to contain it.
Opening and closing old painted windows often can cause the paint to be ground into dust which is then inhaled, so if there is old paint on the windows leave them closed. And clean as much as you can, wiping up paint dust with a wet paper towel and throwing it away, since mopping just spreads it around. After you've wiped down everything, mop frquently.
You can look all this up online, but please take action soon for your daughter's safety, even consider moving to a newer or better maintained house. I've been through this, though at a lower level, and it was scary and overwhelming. Good luck!