I've been trying to teach a couple ladies how to throw backhand, who are forehand dominant (both are very good players already, placing at the top of advanced women division). You're already throwing 330' with a Valkyrie, which is great! It sounds like you have a lot of potential to develop big D, and DGR is the right place to come for wisdom and advice.
Since it isn't easy to build up arm speed, learning to snap a disc out like Masterbeato describes is definitely the best thing to do, for gains in distance (and accuracy) without requiring a great deal of effort or strength. Watching Paige Pierce, Valarie Jenkins, Sharon Jenkins, and other top pro ladies throw I can ensure that this is exactly their method (and they throw farther than 99% of guys). Get the elbow out forward and then use your weight shift, hip, torso, and shoulder rotation to whip the forearm around, keep your hand on the other side of the disc, and focus your violence (summon the grrr!) on the hit point, forcing the disc to rip off your index and/or middle finger. Accelerate through the hit, which will result in a good follow through.
I noticed this great video of Paige Pierce throwing backhand...http://www.youtube.com/watch?v=bBQ4SkpWpRU
...you can really see the disc go into the hit with slower velocity and come out of the hit like a bullet. In that one flash of an instant, the disc gains twice the speed that the arm is able to give it. Snap (aka "cracking the whip") is a speed multiplier, using the leverage of the wrist and fingers to sling the disc out around the pivot, much like a trebuchet. One has to start slow at first, to get the rhythm of the whip, and add arm speed incrementally until the action at the hit can keep up with the quicker timing of the motion. The disc is part of the whip...you literally whip it so hard that the end of the whip comes flying off in the process. This is an athletic motion, and requires training and drilling. Experimenting with different weight discs, harnessing power from your torso, etc., are all important elements.
Many of us on this board are still working on developing big snap, and for a long time much of the discussion has centered around this very topic. I'm only "half-hitting" it, able to get over 400' but still working on "full hitting" to get me up to 450'-500'. Masterbeato got it a few years ago, and absolutely crushes. Blake T's kung fu is very strong.
Anyways, welcome to the DGR quest for bigger snap!