I even resorted to eating her out, which I had never done before, but to no avail.
Whoah horsey - you went AS FAR as giving her Oral!!!
That is probably one of the most powerful weapons in your arsenal.
I had a playmate visit for a few days recently and despite knowing from Day 1 that I would get laid, I played it cool and made sure there was lots of foreplay prior to fvcking her.
One of the teases was Oral Sex - she had 4 orgasms from that and needless to say, when we actually had intercourse she had several more.
Give her a good half hour of oral - explore all of her vagina, give her a vaginal massage as part of it (massage her labia with your fingers the same way you would her shoulders or back) and make her feel yummy.
While licking her ****oris, insert a couple of fingers inside her and massage her G-spot - the two sensations combined will drive her wild.
All that said, some women have difficulty achieving orgasm, but even the most tense woman can *** if you take the time to really explore her well.