You and your daughter can start by having them both on leashes in the front yard. Let them meet nose to nose or nose to butts whichever they prefer. Pay close attention to the reactions which will probably go in this order: hair on hackles standing up, tails raised, standing stiffly on their toes while eyeballing each other, and if you're lucky, play postures. If you hear any growling, calmly but quickly pull them away from each other. Don't let them get the leashes twisted or a fight will more than likely happen because they feel trapped.

Don't try to force a friendship, not all dogs are compatible with each other. They don't have to get along to live in the same house. Instead of chaining the Pit out front while the Lab is out back, rotate them. Let the Lab have his time out back, bring him inside, then let the Pit out back or take her for a walk. If you're leaving the Pit chained even if it's not that long, there is too much room for tragedy: she could get stolen, attacked by a stray dog, get caught up in the chain or even hang herself.