We were pretty consistent signers in our house. We learned the signs and signed with the kids whenever we spoke or read to them -- so they learned from us, not TV. Both my kids had about 200-250 signs before they could speak, and put 3 signs together as well. My son spoke a little late, and almost immediately was forming sentences. My daughter spoke a little on the early side, and was making full sentences by two.
Having researched this, there is no evidence that signing will cause a child to delay speech. A child who "loses" words or milestones should have an immediate developmental evaluation -- that's really not a normal thing. Reassuring, though, that she is putting two signs together.
The experts at the American Academy of Pediatrics recommend no screen time for the first two years of life. A few reasons: having a TV on in the room results, on the whole, in the parent not speaking to the child as much -- and talking to a child is REALLY important developmentally; too much TV has been associated with attention problems in some children. There are also concerns about whether the rapidly changing images might cause changes in the way the brain "wires" itself.
There's nothing wrong with letting her play by herself with the toys or dog or tuperware and wooden spoons. It's actually much better for her, developmentally speaking, than too much screen time. She doesn't need constant constant attention, especially if she can entertain herself for a half hour at a time.
