Amanda, you are in a good position to have some sort of dialogue with the SCBU about this, in a prof capacity.
Unless this mum has been expressing about 8 times/24 hours since the baby's birth (and I bet she hasn't - so few SCBUs really support this), it is highly unlikely she will now have a good breastmilk supply (I am guessing the baby is now about term?). A 33-weeker is prob not able to take anything like all his nourishment direct from the breast - the co-ordination of sucking and swallowing doesn't take place until later - so the baby would definitely have needed EBM on top of whatever he could have got at the breast.
Yes, knowing the baby has had a certain amount of calories can be important with pre-terms - giving measured EBM would have allowed this. In fact, she would prob have produced more EBM than the baby needed, if she'd been expressing often enough. No matter - it could be frozen, and it can't be emphasised enough, fewer than 6-8 times a day expressing (and the night time expressings are really important) and the breastfeeding may not get established and maintained. The idea is to fool the body into thinking it needs to produce milk for a term baby, so the expressing has to mimic this.
Anyway, if the mother is using the breast direct, then it would not be at all surprising for the baby to lose weight - the milk is just not there, and will not be there unless she starts removing it, one way or the other, effectively, 8 times in 24 hours. I would actually be very concerned about this baby, and the milk supply...the baby should be gaining weight like billy-o now, not losing it (and I would not be overjoyed by the 1 ounce gain - unless it really is the start of a turn round, and you can't tell yet). The baby should be skin to skin with mum 24/7 if poss, and she should be putting the baby to the breast at every possible opportunity - and someone should check the baby is not just at the breast, but is actively transferring milk. Ideally, she needs to see a clinical lactation expert, but there are hardly any of them! The baby should be pooing several yellow poos every day, and weeing plenty.
It's good she has you rooting for her, Amanda
With a bad start, though, and that poor support in the SCBU, and her low confidence, it will take a massive boost for bf to be saved, to be honest. Physically, it is probably possible to save it. Emotionally, it may be more difficult.
Whatever happens, the SCBU need to know how to support pre-term bf, and they seem not to.