Thanks for the question. Well, there are two possibilities here, but one of them is not so flattering, however is really not all that bad and can be turned into a positive rather easily.
First, there is the slight chance she doesn’t cum from clitoral or G spot stimulation, or a slightly larger but still small chance that it is just really really hard for her. This may be the case and you may be doing everything fine.
Most, and by most, I mean well over 90% of guys, are just bad at eating pussy. I am a man of statistics and my bet is on the latter – that you have a lot to learn about eating pussy. Good thing is, you can be a pro by the end of the week, make her lose her fucking mind, and feel like Rocky climbing the stairs.
First off, key is getting at her clit and sustaining a fast, rapid, wet, pressure on her clit. Suck it. Flick it with your tongue as fast as you can. No need to be super soft here. Be firm. Change it up but never ease back on her clit. Put her clit between your lips and tongue and stay at it. As fast as you can go.
Spread her lips when you do it. The clit has a fold (aka clit hood) that slightly covers it from the top so by pulling back her lips and clit hood, then providing a fast and intense tongue movement, you are essentially exposing the most intense nerve ending area on either a male or a female. It has as many if not more nerve endings that the entire penis. Imagine what she must be feeling.
Stay at it until she is flipping out and then kneel up a tad, twist your head, keep your mouth over her clit, keep doing it the same, and slide two fingers in her upward to reach her inner wall and hit her G spot. Do a ‘come here’ motion with your fingertips while eating her.
If you do all that, and she still says you are not good at eating pussy, then she is nuts. Most girls have guys licking their lips and hole like idiots and totally missing the important part.
Last, stay at it. Don’t stop until she cums. That is one of the biggest mistakes guys make. Just give it time. No girl will turn away that kind of action because it’s taking awhile.