I split fed my twins (forumula, EBM, breast) and although it wasn't as ideal as exclusively breast feeding them I'm very pleased with what I managed. I think a LOT of twin mothers give up on breastfeeding just because it's so damn difficult to do for two babies. Not impossible, but it needs cooperative babies with good suck reflexes, support and patience - all of which can be in short supply in the early days and which can feel like just TOO MUCH when you're sleep deprived and struggling with the whole twin marathon.
I was never able to make one twin wait whilst the other was fed and actually threw Gina Ford's twin book against the wall when I read her section on suggesting that. The idea that I'd have been able to feed one twin whilst the other screamed blue murder in her cot or in a bouncy chair was just laughable. It would have been incredibly stressful and whilst a dummy can help slightly the idea that she'd have sat there peacefully waiting for five or ten minutes.....
I had help in the night (husband and maternity nurse) and even we muddled through in extreme tiredness. However, on the occasions that I was on my own I devised a very cunning means of feeding both at the same time. It took some practice but it enabled me to feed both babies (premature so with a really weak suck reflex for the first couple of months - they took around an hour for each feed until they were ten weeks old!) at the same time. BAsically, I'd pop one baby in a bouncy chair or on the sofa next to me and place a cushion and some towels to the side of it. I'd then balance a bottle (either formula or EBM) to the side so the baby could turn its head slightly and feed. The bottle would be propped by the cushion/towels/muslin cloths and I could feed another baby (either breast or from a bottle). I'd swap the babies at each feed so they each had some 'me' time at the feed. It didnt' look particularly glamourous and it took some practise but, by God, it worked. When the baby prop feeding needed winding it would just turn its head away from the bottle and I'd be able to lift it up and wind it without dislodging the other baby. It's not orthodox and NO books recommend it but I know a LOT of twin mums through my local twinsclub who've done the same thing. YOu obviously can't leave your babies alone to do this and you need to be prepared if one of them has a little splutter whilst they're feeding, but it DOES mean that you can feed both at teh same time.
It took practice - a good couple of days of trial and error with towels and lots of muslin cloths bunched up but it did work and that was all that mattered. It's never particularly glamourous with twins and I think it's often about not much more than muddling through. But this might be worth a go and it would certainly enable her to keep going with breastfeeding/split feeding if she wanted to as it would free her hands for this.
If she can't get the hang of this I'd also recommend the EZ pillow as it's very stiff and offers good support for feeding both at the same time. I used it but struggled a bit as mine had very weak suck reflexes and it was very hard for both of them to stay latched on at the same time as they both needed a lot of support when feeding - if one broke off needing to be winded the other would fall off and all hell would break loose.....so prop feeding worked better for me.
Hope this helps and sorry its an epic. I just know how hard it can be with the feeding in the early days.
Kx