1. She has a piano.
2. She has two pianos.
3. She has a pianoforte.
4. She has two pianofortes.
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Are they all grammatical?
Do you use #3? What about the plural form of 'pianoforte'? Do you use #4?
The word "piano" is the shortened and most often used form of "pianoforte." I don't hear people referring to pianofortes at all.
http://en.wikipedia.org/wiki/Piano