Am I pushing too hard?

My 8 yr old DD has some learning disabilities, sensory issues etc.... She has made some great gains sense we got her 6 years ago. She is well behaved, loving, nurturing, and a wonderful girl! One of her main issues is that she is not persistent about doing things that are difficult for her. She gives up very quickly and says "I can't" all the time. I have found that a lot of things she can do but would rather have me do for her so she cries and says she can't do it, for example - tying her shoes is difficult for her, her hand - eye coordination is poor and this skill has been very hard to teach her, but we did it!! She has learned to tie, they problem is it takes her a long time and laces often come undone quickly. I am trying to get her to practice but inevitably - every morning - she throws a royal fit and cries and says it is too hard or "I can't" I have to get very stern with her but I get so frustrated because I know she can. I have come to hate that phrase "I can't" We have the same problem with zippers, buttoning pants and even with doing homework. If I really push her she can do these things but she ends up crying, stomping her foot and wanting to give up EVERY DAY - yet she does do it eventually - because I make her. I decided to push her a little harder with her homework - to do more of it on her own with out me giving her any answers, every day homework has become such a hard time!!! Tears, tantrums, time spent in her room to calm down - an hour later, she has it done, mostly, on her own! But we both come out of it emotionally drained and very frustrated with each other! I think that the only way for her to survive in life is to toughen up and do things that are hard. I have given her a lot of grace and lee-way - maybe too much, but now it is time to get in gear and learn these things. I am not asking her to do things that she can not do - I sometimes ask her to try new things, but mainly these are things she has accomplished already. Am I pushing her too hard? I don't want to break her spirit. She has pretty fragile self esteem and no self confidence and she really thinks she can not do these things. The only way I know to prove that she can is to make her do them. any thoughts or advice?