Actually just watched it for the first time, glad you asked.
Some thoughts...
The races played out very differently. 14 girls in Cooks race, but she got a great start and almost immediately had separation with Perez and Shea leading her until just before the mile. Contrast that with Frias who toed the line with 28 girls and got a less than ideal start being boxed in the first 350m or so (chopping her stride, pushing with a few girls due to lack of space) before moving out to lane 3 and accelerating up to the front to go through the first lap in 78.5 v. Cook getting out in 72.7 running on the rail the entire time.
Perez and Shea were still within .5 seconds of Cook (1 length gap from Cook to Perez) with 1200m to go. With 1200m to go Frias had about a 4 second gap, which might not sound like much but that's what I'd call actually being solo, whereas a 1 length gap is not.
Watching the last lap you see Cook biting her lower lip a few times, just a slight grimace and nothing wrong with that, but she appears to me to have dug a little deeper than Frias.
As for indoors being slower than outdoors, it doesn't always work like that. Especially when you're talking about a 6 lane indoor track with very mild banking. Keep in mind there are quite a few runners that have PRs indoors like Rupp in the 800/mile/3000 and only 2 seconds slower in the 5000 indoor, Cheserek has prs indoor in the 1500/mile/3000 and only 4 seconds slower in the 5000. It's not like the "old days" when indoors was almost universally slower than outdoors.
And Arcadia's track isn't the fastest outdoor track around by any means. Azusa's is certainly faster, which is where Frias went 4:35.06 for the mile.
Having watched the NB race now, I definitely think Frias could be very close and possibly outkick Cook if she could stayed attached long enough.
Any ideas if Ellie Shea is racing outdoors? Looks like her last race was that NB Indoors 2 mile on March 13.