biting? can someone help me please?

[tanya+selina]

I have had my 3 and half yr old tb mare nearly a year now and from when i bought her she has always been so moody. She is constantly trying to bite me not just when i put her saddle on but its more when shes tied up? is there any suggestions that anyone has used and has worked to stop biting please? im really sick of not being able to trust her now and i know she is a sweetie deep down?
any suggestions would be appreciated
thanks

 

[Sugarplum Furry]

Are you saddling her to ride her? Or just for groundwork?

 

[tanya+selina]

for riding but it isnt just when i put a saddle on her i could juts have tied her up and she will try bite me for no reason? i dont understand why. I thought if it was just when i put her saddle on i would guess it was poorly fitted but its not just then its doing everything with her??