haven't read teh whole thread so apologies if i am repeating.
personal experience was that i had gestational diabetes, dd was born at 35+6 after going into labour spontaneously.
delivery was complicated and i was on a sliding scale - insulin in 1 arm, glucose in the other.
failed ventouse and emergency c-section.
dd was 8lb 14oz and i put her to the breast asap skin to skin.
midwives insisted she have formula then breast top up.
11 hours after birth dd's blood sugars went down to 1.8 and she was taken to scbu overnight.
they put a feeding tube in her nose and promised to get me for the 2am feed.
they didn't. my buzzer didn't work and at 4am they finally brought another woman on the ward and they absolutely promised to get me at 5am for the next feed.
they didn't - or rather they came but said i was sleeping.
in scbu they fed her with a bottle so no need for the nasal tube.
i was finally taken upstairs a bit later on and put dd to the breast.
she latched fine and seemed to be doing okay. they agreed to bf then ff top ups.
in the next few days dd came more and more easily to the bottle and less easily to the breast.
when i got home it took 10 days and a lot of support from bf midwife counsellor to get dd off the ff entirely.
afterwards i found that i was within my rights to refuse all formula and persevere with bf but i didn't know this at the time.
dd is now 14 months and still bf and thriving. i really wish she'd never had formula or at least that if she had it would've been my informed choice.
but, you just never know how things are going to turn out. i am much more angry (still) at the lack of post-delivery support and the seeming lack of concern or care in getting me to my baby thru the night.
that was the most distressing part altho the work involved on weaning off formula was pretty hard going too.
hope your sil and newborn are doing well and things work out to your sil's satisfaction.
sorry this turned out long!