Edith has to stay put and take one for the team.
Gillian, on the other hand, lives in a time when whales aren't properly valued. People were interested in avoiding war back in the 1930s, but no one* cared about saving the whales in the 1980s. Dr. Taylor won't be missed; she was as valued as Rodent in his time.**
* - Figuratively speaking, of course.
** - Obviously somewhat in jest, but there is this subtext there, if you look for it.
McCoy's jab, "It's a miracle these people ever got out of the twentieth century," can be taken as a biting criticism of more than just their medicine. Besides being environmentally foolhardy (whales, pollution,...), there are swipes at money (obviously*** the use of it at all, not just the use of physical currency), nuclear power, nuclear warheads also, the medicine, smoking, antisocial behavior on public transportation

.
*** - "We've got to find some" in the context of "They're still using money" seals that deal. Otherwise, it would just be, "We need money in the currency of the day."
I mean, it wouldn't have hurt to patch up the transparent aluminum scene with something more solid, like say Scott remembering the actual name of the person who invented it, and it being the name of the man they gave the formula to. That's fair.
They need Dr. Taylor though to save those whales once they get to the future. So that would have been a calculated risk, anyway.