Aw, bless you for doing this important work!
Do you have any idea how long at a minimum you'll have her for? That might make it easier to decide whether you want to move faster or slower toward a new EASY schedule.
Also, depending on her individual circumstances, it's hard to say how much of this is her old routine vs the change FROM it, if that makes sense. Do you know or can you tell if there's an element of reflux? I ask because at 4 months she would normally be on more like a 4-hour feed schedule, but reflux can make babies want milk to soothe the acid burn, as I learned the hard way with my DD, whose feed schedule was all over the map until I realized it was less a schedule and more self-soothing the pain in her esophagus.
I'm noticing that you're not able to keep her up more than an hour right now; this may be a residual result of being kept up so late. I remember reading a long time ago that the sooner before midnight most babies get to bed, the better their overall night sleep; not sure why, but that did seem to hold true for both my kids (and still does as tweens/teens LOL).
Is she waking in the night for a feed? Do you by any chance do a dream feed?
No worries, we'll help you suss it out. <3