I'd say to wait the 6 weeks of exclusive BF'ing first tbh and establish the supply to meet babys demands. It can really mess up the supply if you give formula in the early weeks. And often its the beginning of the end and lots of women find it hard to keep up the breast feeding as baby starts to prefer the bottle (not because it is better but because of a faster flow and not having to do as much work to get the milk out).
If there is a specific reason she needs/wants to give 2 formula feeds a day then she can try it but it may well mess up her breastfeeding. I'd really advise waiting 6 weeks so as to avoid nipple confusion and so on and also so as to not mess baby around. Some babies are allergic to formula also.
There is also the having/needing to express when giving formula at those times in the early weeks. Without doing so the breast milk supply may well not establish or will drop off. It needs baby to feed to stimulate it. And expressing very often does not get hardly any milk out whereas a baby can get all it needs. Expressing is not a good indication of how much milk Mum is producing either way.
There is also no sure way of knowing if a formula feed at night will mean her LO will sleep longer at night. And if the bottle is being given by her it may confuse her LO who will want the boob. Its usually better if someone else gives the bottle feeds so as to not cause baby upset etc.
TBH I expressed a bit when LO was around 3 weeks on medical advice and I soon gave up on it. Faffing with bottles, expressing, sterilising and also having to have someone else feed him from the bottle was more effort and I preferred breastfeeding even though it caused me problems (I had health problems after giving birth). I'm glad I stuck with it as its the best thing I've done for my son and its been a wonderful experience. I'd do it all over again in an instant and never go near a bottle or pump again.
If she really wants to do so then of course she should, but she should be aware of the down sides and problems it may cause. Of course, I hope it goes well for her if she does so.