。
She isn't as cheerful as she used to be.
Literal
She [topic-は] former-time as-much-as energy [subject-が] became-not.
ひところ ('a former time, those days') is a vague time-noun pointing to some unspecified earlier period the speaker has in mind. Combined with ほど ('to the extent of'), it sets the standard against which the present is being measured: 'compared to those former times.' The result clause 元気がなくなった literally says 'energy disappeared,' but with ほど in front, the sense is 'didn't reach the level she had then' — a quiet, melancholic comparison to a brighter past. 元気 itself is a many-faceted word covering vigor, cheer, health, and spirit, and 元気がない is the standard way to describe being down or under the weather.