Daughter will not #2 on the potty?

My daughter will #1 on the potty but when I can tell she has to potty she will hold it in & constipate herself rather than just go on the potty. We try praising her. She went #2 a couple of times but for some reason got scared to. I feel like an aweful mom. I don't know what to do. Tried introducing more fruits & veggies but she will not eat veggies. So I give her the healthy harvest fruit/veggie drink but that doesn't help. She used to LOVE mashed potatoes & whole potatos now she acts like they are a monster to her. She is 2 yrs & 6 months old. I tried pureed veggies but she doesn't like that either. She eats fruits but not veggies. I am at the end of the rope with this potty thing. I know it isn't supposed to be instant but I have no idea how to get her to #2. She did have the dora playhouse. We set it up & she did #2 in the potty.....then that became outside the potty & eventually not at all. Tried mega encouragment, stickers, a progress chart. I feel like a failure. I don't know what else to do. I have to give her pedi-lax so she can go sometimes. Since I've been giving her more fruits she doesn't have a hard time with constipation. But when I sit her on the potty to #2 she will hold it in & constipate herself......