A.F.
If she can find a La Leche League group or leader, the support and encouragement are crucial at this time. Most likely her milk supply is low because the frequency of nursing is low (low demand = low supply). If she is able to set aside 3-4 days to really commit to increasing her milk supply, she can do it. She should nurse frequently, drink plenty of fluid and eat well. There is a natural supplement that can greatly increase her supply when taken over the course of 3-5 days. It is called Fenugreek and is available in a bottle of capsules. Two capsules should be taken 3x a day for up to 5 days. She should see an increase in her milk supply. It is safe for mom and the baby.
If she can manage, she should completely remove the bottle and the formula, or opt to have a set time where, you or her husband gives a bottle - perhaps in the evening when dad gets home. Personally, I think that if the formula is in the house she will be tempted to use it.
She can also pump for a couple of minutes after the baby nurses. This signals the body to make more milk. There are good inexpensive hand pumps such as Avent or Isis. Even if she really does not get any or much milk out of the pumping session, she needs the stimulation to increase her milk supply. She can also do this in between feeding while sitting on the couch and watching TV, especially on the side that does not have any milk coming out.