K.Z.
Focus on the little potty for now, it is good she will use that at least sometimes. MAybe you could even put it outside the bathroom door in the hall so it is not so close to the big one? Then gradually move it closer.
Not only let her see you using the big potty, but also any little friends, cousins etc who might be willing to let her see them too. Once she gets comfortable with the little potty she will eventually move to the big one, maybe you can put her potty seat on top the big toilet for awhile if the size is what is bothering her. Just take it slow, she'll get there.
K. Z.