Also my guide:
http://smashboards.com/guides/outsmarting-mother-brain.343/
Top 3 tips:
1) Stop rolling (for the most part), use short hop air dodge (SHAD). You can land a bair out of it, and that is a kill move.
2) Learn to upb OoS until you do it on reaction. This replaces your shield grab against most attacks (if they are spaced close enough to hit). You can still grab really laggy attacks.
3) Pummel once whenever you land a grab.
For kills, you basically have bair, CS, fsmash, and upb for direct kills.
For gimps, you have fair, nair, dair, uncharged shot, etc.
Shield breaks are a realistic strategy against someone that shields a lot. A shield break is death against samus starting at about 30% (depending on character) because of the dirty bomb: