So I believe she is forward.
When she is supple she can bend either way through her back and neck when I ask right?
The neck will bend regardless, so it's not a good indicator. Often times the neck bends too much and tricks the rider into thinking the horse is supple. Also, you have to make sure the horse isn't escaping out the shoulder or haunches and again tricking you into thinking they are supple. So double check.
we have problems with rhythm though, how would I go about improving this?
Try riding to music. Something that fits your horse's trot...nothing to garrish and loud. Something that's soothing for both of you. Or, you can even ride with an IPOD.
Rhythm is often times disrupted by rider core weakness. Every shift of weight by you affects the horse, so it's important you always be 'with your horse's movement' not against it, UNLESS you are trying to change it...as in, if you were to post slower to slow the horse down. Get in a rhythm yourself and the horse will follow.
Ride long straight and long sweeping lines rather than circles and other tighter figures. Then when you've established rhythm, try a very large circle and straighten if/when you lose the rhythm.
Also, rhythm can be disrupted by asking for too much from the horse. A rider can run a horse right off its feet so to speak and throw it off balance. It's okay to test the boundaries to advance, but always know where those boundaries are for your horse.
'Be' with your horse, not a rider on a horse.