How did she handle with your LOS? given the location I'd have thought a less hostile medium sized character could have sufficed for those 7 seconds.
Then it also depends on your build.
That was something I considered before going in. I was debating Lily vs. Veronica and Rex vs. ED-E because while I wanted a tank, I didn't want a companion that would charge in at full speed and alert every deathclaw in the cave. I decided on Lily because I ABSOLUTELY needed a companion I could hide behind (think I set her to passive to try and prevent her from being too aggresive) and ED-E because if she did charge in ahead, I'd prefer to at least know how many are around the corner before I go in after her.
It ended up being a wise decision because at the very last room with the Legendary Deathclaw, while she DID end up alerting it and two other deathclaws, she was capable of tanking all three for a decent length of time. I think I finally healed her around the middle of my second Turbo dose (so 23 seconds in in a slow-mo fight?) I just Turbo'ed and started firing at the deathclaws like crazy as she and the Legendary Deathclaw fought in slow motion, her sword and his claws swinging dramatically like some gladiator movie. The thing is, Lily gets staggered much less and her reach is very good, and she also pushes her target back some with each swipe. Veronica on the other hand would get staggered more, CANNOT compete with the Legendary Deathclaw's reach and even if she did have pushback it would work against her. I'm pretty sure that if I'd picked Veronica, she would've died and I would've had to kite the Legendary Deathclaw back.
Judging from the Wiki, Lily can get 1700 health, if I'm understanding it correctly, though I know for a fact it's at least 1300. Veronica (probably the second best tank companion you can get), if I remember correct, only gets ~400.