Mardy (lovely, but mardy) baby is asleep now.
Just a thought - I'm sure everything's fine (the wet & dirty nappies etc. you describe sound normal. As for a week without a poo - around six weeks exc. bf infants start making more efficient use of bm and there is less waste - some babies start this a bit earlier) but just to rule out ineffective transfer of milk, has your dw had her latch checked by a fully-trained-in-bfing-mw, or a bfc? Some midwives are not actually trained in how to check a latch is right / check positioning etc. I got my latch checked by half the NHS & told 'twas okay before someone realised it wasn't!
Have a look at the bullet points right at the very start of this thread. Is your dd doing all of this?
It's horrible when you have your abilities, especially your "milk making" abilities as it can cut right to the very core of your ability to nurture your lo, called into question. I also hate the way some HCPs use formula as the first solution to every problem. I sometimes wonder if they're in the pay of Milupa!
Have you or your dw heard of "catch down growth"? It is where a baby is born bigger than they are meant to be, genetically speaking.
My ds started life on 50th centile. Then gained weight very slowly until he seemed to even out on 9th centile. Then gained even more slowly until was on 2nd centile, at about 25 weeks. Then a tummy bug (and, I think, weaning) put him onto the 0.4th for a bit, and now he is back on the 2nd again.
So according to "catch down" theory, he ought to have been born on 2nd centile, but due to things like me eating too many cream cakes in pregnancy (oh and IV drip, and being overdue) he was heavier at birth than he ought to have been.
Could it be the same thing with your dd?
Also if you do feel she needs top ups, as long as your dw gets support with dd when she is expressing, no reason to switch to formula instead of EBM. If bottle-feeding is working okay, great - if she seems to develop an aversion to the breast ("nipple confusion") you could try cup feeding the EBM. I have a newborn feeder cup I can send if you want it.