Apologies for the long post—I really need advice.
My daughter is 32 months old and has never slept through the night for more than a few days in a row and for the past 4 months or so she is up EVERY night. She is down to just a one hour nap a day—which she takes happily. She also happily and quickly falls asleep at 7pm and wakes between 7:30-8:00am. This has been her schedule since she was 5 months old.
However, during the night and now EVERY night she wakes at 2am until 4am on average. Much of the time she is talking, singing and sometimes cries for a short bit…this cycle goes on for at least 1-2 hrs. Last month for a full month I took away her afternoon nap—so she had zero naps and was in bed by 7pm…It didn’t work in the slightest. A couple of weeks ago I gave back her naps as it was starting to take its toll on her day and like I said it didn’t make a difference at night, she was still up at least 1-2 hrs in the middle of the night.
Recently I bought the “Tot-clock”…so far no dice. When I bought the tot-clock and she woke up I would go in to remind her that it was Blue and blue meant “sleep” “no-talk” etc. So far the clock isn’t working either.
We never go in her room so I just wear earplugs and pray for her to fall back to sleep each night. In the past I have tried several things; putting a heater in her room thinking that time of night might be colder, going in and with a firm voice telling her to go to sleep, yelling through the walls, and the tot-clock. Now we just try to ignore it and as you can imagine we are exhausted.
My daughter was a late walker (18 mo) and is currently in speech therapy as she only puts maybe three words together. Other than that she has been evaluated at various times in her life all tests are normal.
ANY and ALL ADVICE IS APPRICIATED! 
PS: She has a twin sister who has been sleeping 12-13hrs straight since she was 5 months old. They sleep in different rooms to avoid waking her sister.