How to help sleep through the night

Okay guys - I know this might not be a huge problem to most, but I’m looking for advice/guidance for those that have been in a similar situation.

I’ve been very blessed to have good sleeping babies. My first was sleeping 12 hrs by 12 weeks (I followed the 12x12 book loosely, she mainly just did it on her own honestly). My second, currently 4mo, goes down at 7pm, wakes up at 630am BUT wakes up once at night to feed. (She drinks 4x from 7am-7pm otherwise)

How do I get rid of this one 3AM feed?!? I know that all babies are different, and that once is not a big deal - totally. But I’m feeing like I’m doing something wrong/missing something and I’m going back to work soon and won’t survive on this broken sleep.

Things I’ve tried:

1. earlier bedtime - she’s SO sleepy by 7pm. I’ve put her down at 8pm, 9pm and it’s the same thing. She still wakes up once before 630am.

2. Tried to feed her less at that 3am feed. Usually I straight nurse, but I pumped and gave a bottle and she’s definitely taking like 5oz. If I give her any less, or prematurely stop nursing, she either screams and cries, or wakes up an hour later hungry again. Subsequently, she only drinks 2oz at 7am and then takes her next full feed at 11am. So the morning feed is getting all screwed up because of this night feed.

3. Tried to give her more during the day with 5 feeds - she still wakes up and just takes the same amount from 4 feeds to 5 feeds.

4. Reduced nap times all around - day naps, last nap, everything.

5. Changed swaddles, her mattress, the light - I mean, everything lol

I know this isn’t the 4mo regression because this has been happening for over 5 weeks at this point.

What am I missing? I know the 12x12 book says to move the feed out 15 minutes every night but sometimes she wakes up at 1am, most nights at 3, some nights at 4/430. How do I move it out when her wake up is inconsistent?

We’ve had 2 nights in the last 5 weeks where she has slept from 8-630. So I know it’s possible!

Help!