Every woman can cum from oral, it's just a matter of you doing it correctly. So she is lying to you.
Try this. Have her point to her clitoris in case you do not know where it is located, begin licking her clitoris in an up motion akin to that of a dog lapping up water (you want to flatten your tongue out when it comes out to cover more surface area), use your whole jaw and body for this movement. It is one continuous motion. Your tongue will begin to get sore underneath and it will begin to hurt but do not stop until she cums (also periodically suck her pussy but for brief seconds not too long, more emphasis on the licking). Secondly slide your to fingers into her vagina facing upwards your pointer and middle finger. You are going to do a come here motion, like come over here, the tip of your finger should scrape the top of her vagina so make sure your nails are cut and filed. Your goal is to make sure that only the tips of your fingers are making contact with her vagina in this motion but as a safety measure make sure your nails are cut and filed. Take your left hand and use that to squeeze her butt cheeks along with moving your hand up to slowly rub her stomach, as well as making it up to the top of her breasts to rub her nipples and squeeze her breasts. You want to be doing this all fluently. All you need to know is no matter how sore your tongue begins to get do not stop licking and do not speed up either when she says she is close to cumming. Make sure you continually maintain the same speed and motion. Only thing though is you can increase the intensity of squeezing the ass cheeks or breasts like grabbing and squeezing hard.
