Has she tried having her upper body at different levels? I use pillows or the headboard for support. There are times that I want my head to be on the mattress and others above my waist, it just depends.

SOC you really do say the sweetest things dont you>??

Hey CL if it works, and keeps him happy the syrup can flow......

sort of sticky isn't it???

CL you do know how to crack me up. It's all chatter.....

Is it the idea of doing her from behind or do you really need her on her knees?

If it's just the idea, why don't you go for spooning?

Also, I find that it feels deeper if I perk my butt more.

Why don't you try complete communication during doggie style and slightly vary positions. Try with your leg at different angles or hers at different angles, also try her being on her hands vs. her head being on a pillow. Or even try something that would be the equivalent to her leaning over a counter (I think it feels deeper in this position, but you never know how she feels).

COMMUNICATE, COMMUNICATE, oh and COMMUNICATE!

also use your hands. Is it she feels that she is tight, spread apart her cheeks. Get her mind a little unfocused and massage her cheeks, and no I am not talking about the ones one her face. Massage her spine, get that spot down low on her back that helped with the pain she had during childbirth.
Being on our knees and hands or shoulders ect does not exactly give us the advantage of being in a position for much more than balance. It's a position where you have all the advantage. Keep her vocal how she feels, how wonderful it feels for you. You will find a way.....only if you keep trying to find one.

Spooning or even having her sit upright with her back towards you should make it easier for you both.