Tecfidera is definitely only given to people with relapsing remitting MS. If your wife has PPMS, then she won’t qualify. Even someone with Progressive Relapsing MS can’t get Tecfidera. So maybe you have your definitions mixed up. Possibly the neurologist has said your wife has RRMS and that her disability is progressing. This wouldn’t mean she has progressive MS.
Tecfidera is taken by many people without difficulties. You just have to make sure the pills are wedged in between food, so eat, take a pill, eat some more. And the stodgier the better (porridge is a good one).
The aim of Tecfidera, along with all disease modifying drugs (DMDs) is to reduce the frequency and severity of relapses.
So with luck, your wife will start the drug and have few and far between mild relapses.