Jane Savoie has a really great set of books for overcoming riding fears,
'That Winning Feeling!' 'A winning attitude' etc.
You can try finding them at your local library,
or see if any horsey friends own them.
Another thing that might be useful is to have someone knowledgeable or an instructor lunge you on a line when you first start cantering.
That way you can focus on your seat, your breathing, etc and have someone else focus on controlling the horse.
If the thought of cantering really strikes fear into you, just keep trotting!
Trot is ant important and hard to master gaits for dressage,
so work on perfecting your trot, (posting, sitting, posting w/o stirrups, sitting w/o stirrups etc)
You can also do cavelleti work at the trot, and pole work.
and canter when you feel you are ready,
sounds like you have a nice horse to ride!
Spend lots of time bonding with her,
perfecting your walk/trot work, trailriding etc, and don't rush,
all good things come with time and practice.