I personally don't think anyone needs 8mg. I have a rather large Morphine habbit, and I just went 4 days on one 8mg tab. I cut it into 4 pieces and got 4 days out of it, could've gone longer because technically you only really need to dose every other day.
so really, if she got ahold of some 8mg pills, she could cut them in half, and make it last 3-4 days. but be careful, make sure she's in withdrawals before she starts taking the suboxone.
just the other day, I dosed too early on my subs (I shot 2mg up) and I went into precipitated withdrawals, which is worse than just letting yourself go into normal withdrawals. I really thought I was gonna die for about an hour. I immediately started sweating hardcore, and was very cold, I turned super pale, and then almost grey. ended up passing out on my bed, woke up about 3 hours later covered in wet bedding because I had sweated on EVERYTHING. but when I woke up those 3 hours later, I felt much better, because I guess by then the suboxone had fully taken over. but boy were those 3 hours pure hell. so again, make sure she's in full withdrawal before dosing with suboxone.