My 10 year old has bad handwriting due to dyspraxia - and it is incredibly hard to fix. (Does your DD have Dyspraxia?
This is all I have found out about the causes and interventions so far:
(Your DD may well suffer from all of these problems.)
Visual Perception Problems
(Not leaving spaces between words made me think straight away of this.)
The handwriting course that helps with visual perception problems is Write From the Start. Trouble is - she's a bit too old for it, it works best with kids 4 - 8. Still might work though.
Otherwise I highly recommend getting her eyesight tested by a behaviour optometrist and doing vision therapy if recommended.
Gross Motor Skills
Speed Up is the best program to address these problems. Basically in order to be able to write properly you need enough core strength to sit up straight (does she always slump at her desk?) and enough shoulder strength to control your hand.
Fine Motor Skills
This is problems with your fingers. I suspect because she hates handwriting she means it physically hurts - because of problems with her fine motor skills.
You need to do loads of things with her to improve her hand strength and pincer grip to improve this. Theraputty is what OTs recommend for this.
Daily practice
Has made absolutely no difference at all to DS. Absolutely none.
Now that we have addressed his vision, gross and fine motor skills I am hoping that it will help. But am not all that confident.
If you really want to improve her handwriting you (and she) are going to need to do a lot of work on it. Daily exercises, for a year or 2, to address all of the above.
You could see an occupational therapist privately for help, and get a tailored set of exercises.
Some places offer remedial handwriting courses.