Answer:
Her answer is not reliable.
Step-by-step explanation:
Reliability and validity are two major concepts that are used to assess the standard and quality of response/research.
While validity of an instrument is the idea that the instrument measures what it intends to measure, reliability is all about consistency and whether or not results could be replicated.
While your friend's answer may be valid, it can't reliable because of the differences in her response within a short time.