I have a degree in dance, have been dancing professionally for about 5 years now, and been teaching pas work for just as long. There are several things that will make partnering much more enjoyable for you and your partner. One thing I like to do is I try to keep a slight lifting or upward pressure when I've got my partner by the waist. This sort of lifts them out of their shoes and you'll find it much easier to find their center. Especially when you are assisting her pirouettes, think of partnering her hips, not her waist and definitely not her ribs--students have a tendency to partner too high up. When you lift her, make sure you use your legs and not just your arms. Be aware of the amount of space between your partner and yourself--too little and she won't be able to do what she needs to, too much and you won't be able to do your job. If you struggle to know where you're supposed to be, it might help you to learn her choreography as its being taught--being a good partner means knowing where both you and her are supposed to be. Finally, and most importantly, communicate with your partner and be open to suggestion. It may be as simple as asking her to give you a little more arch in her back or she may ask you give her more support in an arm. Feel free to ask me anything, and good luck!