Use of comparisons in Hebrew
I am learning comparisons and superlatives in Hebrew and wanted to know if this sentence is correct:

אני יכול לדבר אנגלית הרבה יותר טוב ממה שהיא יכולה
I can speak English much better than she can.
Somehow I believe the word ממה is incorrect.

Incidentally, the correct English is always: "I can speak English better than she" instead of "her" (many if not most native English speakers make this mistake), because the full grammatically correct sentence is : "I can speak English better than she can speak English"

Question

Use of comparisons in Hebrew
I am learning comparisons and superlatives in Hebrew and wanted to know if this sentence is correct:
 	
אני יכול לדבר אנגלית הרבה יותר טוב ממה שהיא יכולה
I can speak English much better than she can.
Somehow I believe the  word ממה is incorrect.

Incidentally, the correct English is always: "I can speak English better than she" instead of "her" (many if not most native English speakers make this mistake), because the full grammatically correct sentence is : "I can speak English better than she can speak English"

Answer

Your sentene is correct. The more common (and still correct) way is: 
אני יכול לדבר אנגלית הרבה יותר טוב ממנה.

Answer

Thanks Ramy for the answer.  I had a question on the niqqud however. An online dictionary gives me this:

אֲנִי יָכֹל לְדַבֵּר אַנְגְּלִית הַרְבֵּה יוֹתֵר טוֹב מְמַנֶּה. 
aniy yakhol l'daber an'g'liyt har'beh yoter tov m'maneh.

but I think that it should be the following for "than her"
  mi'maha  nמִמָנה

and for "than him"
  mam'hu מַמְּנוּ

is this correct?  Thanks again!