Poor baby, sounds like a whole lot of things going on there. And hugs for you, things naturally change A LOT at 4 mos, I'm sure it's nothing to do with what you've done!
Is she ill, do you think? If she is, then I would just try to go with her sleep needs. I don't know if you've experience of her being under the weather, but my two always need lots of extra sleep when ill and it does seem to help them get better faster.
The waking up early after BT (30 or 45 mins) and screaming is something my LO1 did around this age. It was a sure sign of OT for us, and it was rock hard to get him back down. I'm conscious that she's an angel baby and they will just go along with things until they can't cope any more, so perhaps it'd be worth scaling back A times for naps and seeing if that helps her a bit.
I'm interested by what you say about her different behaviour to her brother - maybe her 'tired' just doesn't look like it, more like wound up and ready to go? That's a clear OT sign here, strange as it sounds.
Slightly OT (off topic), but I'm intrigued that she's BF and going 4.5 hours between feeds. I assume she's having top-ups too? If not, I am truly amazed! You might want to up the tempo of daytime feeds, if you think she's having a growth spurt, but you can also expect a couple of NFs.
