I stopped the df at 4 mos and dd slept through to 7:30-8 am and has ever since.
As for her not eating well during the day, do you have a quiet, dark place to feed her? Also, how long is she going between feeds during the day?
If you want to break the 4 am feeding habit, you could try pu/pd. It will take several nights probably, but if you commit to it, it can work. Then, after accomplishing that, she'll probably last longer before waking up in the morning as long as she's eating well during the day and the df works out. If you'd like a reference in the BW book, I'm looking at pgs 120-121.
You want the lo to get a good feed at the df so that they can last through the night. This would mean stimulating her suck reflex, but when it comes to the point that she just won't suck anymore I'd put her back down. This is how I knew when my dd was ready to give it up. She wouldn't barely suck for 5 minutes, and she used to feed for 20-30 at the df (I fed both sides).
Do you want to post a typical day's schedule for us to look at and offer advice?