My new partner is having trouble climaxing..

Hi. I'm 25 and I'm casually seeing a girl a couple years younger than me who I can't seem to get off (cum).. We only had sex a couple times, since our relationship is pretty new. She seems stiff in bed like she's uncomfortable, but at the same time she moans and touches herself - so I know she's enjoying it. I also talk to her to make sure she's feeling good. It's almost as if I have to physically move her around when switching positions.. kind of uncomfortable for me. She tells me she's had trouble reaching orgasm before. I've given her oral sex for a quite while and she told me she came, but I don't believe her because it was the first time we were together and saying NO would've been a little awkward. I'm sexually experienced. My ex used to cum at least 5 times everytime we had sex.. so this is a bit of a shock to my ego lol. I just want to make her feel good, but she insists that it's ok that she doesn't cum.. I don't agree at all. to accept that is ludicrous!! so.. any advice???