Hi
keep pushing those A times, 2hr is appropriate at 4 months and the average kid is moving towards 2:45 to 3hr A times at 6 months. You may find just jumping to longer A times rather slowly increasing is the way to go when you're so far behind the average A times as otherwise you'll be tweaking til she's 9 months old. All this is presuming she was not premature.
The most important A time to increase is the first one from wake up, that encourages her to sleep longer in the morning and also gives her the best chance at a long first nap.
Check out the links about 3-2 nap transition, see if you can find a model routine that you think may work and give it a go. Once you've done that for a week or so, you should be able to see where to tweak to suit her.
Hugs, the sleep disturbance thing is really hard.