Point out to your friend that if she stops she will have to care for a newborn, entertain a toddler and wash, sterilise and make up bottles, and that will be much harder work!!
If you can help her get through the first 6 weeks (which is the hardest bit) she should find the feeds start to space out a bit and it will get easier.
She probably just needs gentle encouragement, practical support; take the toddler to the park for a couple of hours, cook a meal or provide some easy to eat snacks, do a load of washing for her, that kind of thing. If you can keep her spirits up, tell her what an incredibley good job she's doing, how briliant she is etc, over the next few weeks she'll find it gets easier and suddenly isn't such an uphill struggle any more. Thats when she'll start to reap the rewards, bf'ing is so easy then, baby chunters, you pick it up and put it up your jumper and read a book to your toddler.
She may find a nice sling helpful too. One of my friends used to come over and play with DD1 (2.5) whilst I was feeding DD2, then hold DD2 as she slept whilst I played with DD1. It was enormously helpful, and having another adult in the house once DP had gone back to work kept me sane from a conversation point of view too!!
You sound like a really nice supportive friend, well done for being there for her.