So sorry you're having to deal with this...ugh, worms are yucky, I know. But you will get her better!
Honestly, she could've picked them up just by sniffing the poo on the ground from some other infected dog. But, with you saying she's *always* had issues - I then think she got them from her mother, since birth. Poor baby. If that's the case, she has had them a long time now - and they've likely really done a number on her small intestine. And if she's auto-infected herself during this whole time (not unlikely) -- that infection tends to be worse and the worms may burrow into the colon.
SO, be sure to treat her aggressively with your vet. And, I'd get her on a good probiotic ASAP to repopulate her intestinal flora - there are many probiotics out there - I like Natures Farmacy Dogzymes -
here.
Keep us posted and just know she'll be okay. That said, if she's had these since birth - it could take a good while (months) for her poo to normalize to due the damage done in the small intestine. If you keep having trouble w/ poo, be sure to post here for help! Many of us have been thru that.