My wife and I worked at this for several months until she squirted. I used the 2 finger method. Fingers slighty curved. Lots of lube and vigorously finger bang her. Not aggressive but rapid. She was on her back, pillow under butt and legs up. Recommend a sexy spreader to help take the strain of holding your legs up.
Being very aroused helps too. Maybe even throw back a few drinks for fun! I've also heard being well hydrated is key.