DS first smiled around 5 weeks but they were few and far between for a few weeks. He also didn't like is play gym until around 3 months. I think they are just too small to get enjoyment out of things like that. They haven't figured out their hands yet etc. In a couple of months your DD will more than likely bashing the toys about on her play gym.
It seems fairly common for young babies not to like tummy time. But, short frequent bursts of time on their tummy is apparently better than longer periods of time. My DS is now 5.5 months and only in the last few weeks he has started to enjoy a bit of tummy time (but only if his nappy his off!). Not sure when the cooing started, but I think it would have been closer to 10 weeks.
One thing I have learnt since becoming a mum is that all babies are different and do things at different times. Try not to stress, and if it something that is really worrying you then speak to your MCHN or GP. In the mean time, enjoy your little bundle. Spend lots of time cuddling and interacting with her. Time really does fly and I am sure she will start showing all of her new little tricks soon.