89 yr old in hospital on aspirin clopidogrel and warfarin for stroke and heart attack has had another stroke and blockage seen on Brain scan and swelling left side of brain how come while on so many thinners is it possible?

Yes, it can happen. For several reasons, the case isn't easy, and it seems that there is lot going on. I trust that the hospital and the treating doctors are doing their best, wish you all, the best.
Unfortunately. some "strokes" are BLEEDS... Speak with her Neurologist More information needed Hope this helps Dr Z.