It is perfectly normal at 5 months to need a NF or 2 even with a DF. The DF is not intended to necessarily allow a baby to STTN with no NF, it is intended to skip the 1/2am feed and move onto the 3/4am one. It does sound like she is hungry if she wakes at 3am and is complaining every 10-20mins, that is definitely a hunger sign if she doesn't settle, so please go ahead and feed her
My guess is she'll feed nicely and be straight back to sleep in no time, which means more sleep for baby and mommy.