"In BrE, when they put a verb after as well as, they most often use the -ing form. (См. Swan M. Practical English Usage, Oxford, 1997) source"
One subject here: (as well as means and)
She sings as well as playing the piano.
She sings as well as plays the piano.
As well as playing the piano, she also sings.
(= She not only plays the piano, she also sings = she can play the piano and she can sing.)#1b
He was a real scholar as well as a great composer.
(= He is not only a great composer, but also a real scholar = He is a great composer and a real scholar.)#1c
He is intelligent as well as good-looking.
(= He is not only good-looking, but also intelligent = He is good-looking and intelligent)
Two subjects here: (as well as means to do both things equally well)
She sings as well as she plays the piano.
(= Her singing is as good as her playing.)