Final answer:
Stella's sister can drive with an out-of-state license for up to 90 days in Texas but must obtain a Texas driver's license if she intends to stay and drive beyond that period.
Step-by-step explanation:
The subject at hand is whether Stella's sister can legally drive in Texas with an out-of-state license for a duration of 4 months.
According to Texas law, individuals moving to Texas who have a valid driver's license from another U.S. state or territory are required to obtain a Texas driver's license within 90 days of establishing residency.
As Stella's sister plans to stay for 4 months, which is beyond the 90-day grace period, she would need to obtain a Texas driver license to continue driving legally in Texas after those 90 days.