She will be eligible for COBRA from employer 1 to continue that coverage after that employment ends.
She has 60 days to sign up for this COBRA coverage which will apply retroactively to the day she loses the employer-provided coverage, so she waits to see if she needs it.
If it turns out she needs the COBRA continuation coverage to cover something that happens before employer 2's coverage starts, then she signs up for COBRA and pays a month's premium. While it's expensive coverage for the gap period, she doesn't have to sign up and pay for it unless she needs it. Stay safe.