Yor may find that her tired signs are not obvious - I used to find it hard to pick them when DS was that age. She may get jerkier movements, red eyebrows, be grizzly, look away from you, stare into space, lose interest in toys?

You may have to teach her how to sleep - use your sleep cues (music, wrapping, dim room) & stand by her cot patting/stroking her until she falls asleep (so she gets used to falling asleep in her cot rather than on the boob). Once she will start to sleep like this, you can gradually withdraw the amount of patting (eg. let her lie there for a while, but if she cries go straight in and pat until she is calm, then go out again until she cries, then straight in & pat).