Hmm...I doubt the tank is cycled. It sounds like it sat empty for a while not long ago, correct? Without a constant source off ammonia, the bacteria will die off pretty quickly. You're probably just in the beginning stages of cycling right now.
When you get your water tested, ask for specific numbers rather then just an 'okay' or 'not okay' and make sure they're using a liquid test kit, not the strips....the strips are notorious for being inaccurate. And while having some place to get your water tested for free is a great resource, its also a good idea to start saving up for a water testing kit for your own if you can't afford one right now, it will save you a lot of trips into your LPS while you're in the process of cycling, which could take a couple of months, and its always great to have the option of testing your water right away in case something goes wrong so you can eliminate/deal with any water quality issues.
Unless the plant dies and rots(which so long as you get a healthy one and you've got good lights, shouldn't be an issue), adding live plants would definitely be much more beneficial then not. Have you checked out are Planted Tank section here on the forum? There is a TON of great plant info over there.
I know girlies and shorter finned males can be a little more quick and active....does she look like shes darting/scratching against anything? Or breathing heavily at all? How is her color?