BUT
For 2020 there is the issue of the stimulus payment. If she is your dependent, for 2020, she doe not qualify for the $1800 stimulus, on her own return.
You get the $500 other dependent credit and maybe some EIC, but she misses out on the $1800.
Technically, it's not optional. If she qualifies as your dependent, she is not allowed to file as a non-dependent.
