try increasing the foreplay. get close to orgasm before entering her, if this means you need to masterbate yourself...then thats what it means.

talk to her about this and dont make a habit of it, but in order to get the monkey off your back, but try not worrying about pleasing her, have a good time, climax....then you can make sure she cums later on...with your hands, tongue...or till you're good to go again.