How long is it taking her to get to sleep.
By the looks of it she is about 30-45mins less sleep on the new routine, so maybe she needs an 8pm bedtime. Or maybe she just needs a longer wind down routine
Also without having her siblings at home with her during the day maybe she isn't as stimulated & so isn't as needing of sleep, a lot depends really on how happy she is, if she takes longer to go to sleep but is happy all day long then maybe she's taken a developmental leap & needs less sleep.