Well, are your feeds like this right now: 6:30, 9:30, 12:30, 3:30, 6:30? Basically, you want to fuse together 2 of the feeds gradually. So, you could try 6:30, 9:45, 12:45, 3:45, 6:30, then, 6:30, 10:00, 1:15, 4:00, 6:30, then 6:30, 10:30, 2:15, 6/6:30, then 6:30, 10:30, 2:30, 6/6:30. If she has a harder time eating as soon or can't wait long enough for some of the example times, feed her when you feel she's ready. You may find that she'll fall right into a 4 hr routine without a fuss. My dd transitioned by sleeping past a feed one day and we never looked back. I set it as her new nap and feed routine and it worked fine.
You're doing fine, just remember to take notes so you can find what works and what doesn't.