My DD is an outdoor girl, so we do a lot outside. Whether it's drawing, painting, gardening, playing with the dog, playing on her swing set, going for a swim/walk etc. Whatever you're doing with her, once she's happy doing it, gradually give yourself more distance between you and her. Until it gets to the point that she is happy doing it herself, while you sit back and watch. Eventually she will be happy to play on her own. It'll just take time.
Like Kimbaz said, FDC or childcare is great. My DD goes 3 times a week and loves it.