S.H.
You know... my daughter was very similar. NO method, would work with her. I tried.
The only way she would settle down or sleep was if I was right next to her AND I had to keep to a consistent routine pre-sleep and pre-nap. EVERYDAY. And so sure, I co-slept with her... and my son now, as needed. But my son is way easier.
What you could do, is try "Hyland's Calms Forte- for kids." You can get it on amazon.com or any natural food store. I used it for when my kids are sick or teething. It's homeopathic and has no contraindications. BUT, I'm not sure if you can use it on a 12 month old...
Next, every child is different. BUT, some babies/children are just more 'sensory sensitive'... and this really throws a hiccup into things, including sleep. I know this because my daughter is this way... she is very "aware" of & sensitive to her surroundings/noise/temperature. And no, crying it out... does NOT help for ALL children. It is NOT a magical method to MAKE kids sleep. Out of desperation with my daughter, I and my Hubby tried it, in varying versions, and NO MATTER WHAT WE DID, it did not work. Not with my daughter and her personality. So you see, there is no magic "template" that crying it out will work.
Next, YES... for both our kids, for BOTH night-time AND day-time... we use the SAME routine for sleep/naps. You have to keep it consistent. Even with my daughter who was very difficult... the ROUTINE was the thing that helped. THIS is key. For me, and dealing with the hardship of getting my daughter to sleep since birth, I just "learned" to go with what is best for her and for what works for her. Not me.
Next, bear in mind, that your daughter will one day sleep better and become more consistent about it. BUT... in HER own time. YOu can't really force a child and make them sleep, if they can't. EACH child is different. Some just can't self soothe very well. My daughter, didn't sleep well until she was about 2.5-3 years old. I have not gotten a full nights sleep since she was born... and then, by the time she did become able about it... then I was pregnant with my 2nd child... and I STILL don't' get a full night's sleep.
Next, there are all kinds of perspectives about it and approaches.
But you rule out the obvious: (1) is she getting fed enough during the day time? a hungry growing child will not sleep well... and 12 months old is a growth-spurt time. (2) Is she teething? (3) Is she STILL recovering from her illness? have you taken her to the Doctor for a follow-up? (4) does she have gas problems? (5) ear infection? (6) is she allergic or have any food intolerances? (7) Is she developing on par? (8) do you still have milk in your breasts at an amount that is enough for her? (9) Does she indeed latch on properly? Many times, if a baby does not, THIS is why they can't sleep because they are not getting enough intake from the beginning. - Does she eat enough? (10) have you given her a "lovey" to sleep with? Then she can use it to self-soothe... or a pacifier? (11) DOES SHE TAKE REGULAR NAPS? -the thing is, a baby/child that does not nap, is actually harder to put to bed at night... because an "over-tired" child is actually sleep deprived and it causes sleep disturbances and it actually makes them wake MORE and sleep quality is worse. So, I would make sure, she has regular naps, at scheduled times. (11) do you allow her to "wind-down" first before bed? Children NEED to wind-down first... it takes me 1/2 hour for me to wind-down my kids before bed and naps. I turn off all extra noise/extra stimulation and make the room dark etc.
So many things to consider.... each child being different.
And believe me, 12 months old is a major time of developmental leaps and growth spurts as well.... both physically and cognitively. SO, this throws a wrench into sleep patterns too. It is common that at certain age junctures.... sleep patterns change. It's normal. BUT you said your girl has been this way since birth.
Anyway, just some thoughts and what I went through with my daughter. Who now, by the way, is a great sleeper and goes right to bed on her own and falls asleep within 5 minutes of hitting the pillow! For her, it's just the way she was... and it was just her. Nothing we did could have "forced" her to sleep on "our" terms. The only thing that served as some kind of consistency was the bedtime/nap routines and my being near her as she fell asleep.
All the best,
Susan