Typically Tracy recommended waiting for a four hour EASY until your baby is four months old, however if your baby has low sleep needs, she may be ready earlier. That's really a decision only you can make, as you know your baby best.
At three months, I was starting to wake DS once his naps hit the 2hr mark. I did this because I didn't want to steal sleep from the night time but if you're daughter is sleeping well at night, I see no reason to change your current routine.
I would definitely get baby out and about if the weather allows for it. Firstly, it's good for both you and DD, emotionally and psychologically. Secondly, there are so many new sounds, smells and sight for your DD to explore. Yes, she is still very little and may fall asleep but if you take her out 15-20 mins before her nap begins, and try to keep her up for that time by showing her flowers, grass, bees, etc. it's perfectly ok for her to then drift off for her nap and you can enjoy a nice, long walk and possibly a good chin wag with a girlfriend.
Try not to let fear hold you captive. It's hard with your first but if you can try to just enjoy all the little changes and experiences that come up, it's so much more fun!
