You can absolutely be an environmentalist and not think that the lives of individual animals matters. I'm reminded of nature documentaries that will sit and watch an animal starve, because that's the natural thing and they are not there the interfere. I don't think this viewpoint is horrific.
"maybe because coming from an environmentalist, who are supposed to be the good guys" I think you should look at why you think these people are the "good guys". By the sounds of it, sorry if i'm wrong, but your thoughts on environmentalism comes from a place of empathy. You look at individual animals and empathise with there suffering. And by the sounds of it, you expect everyone else who considers themselves an environmentalist (which I also would say I was), to also come from this place of empathy. However not everyone does, and this isn't horrific, people just have different priorities.
I don't know about what else she said, but "animals only have value as things exploitable by humans" doesn't necessarily follow from: 'species matter individual animals don't'. Personally I think animals have a value completely apart from people and are even more valuable when they have no interaction with humans at all.
Q. Why kill other sentient beings at all A. Because in many cases it is necessary for the survival of the species.
i.e. offering "help them survive" as a reason to kill them.
ps Some of the other descendant comments are very troubling, and remind me of what I heard a young female environmentalist say at a political meeting once, that "individual animals don't matter, only species matter." (i.e. the loss/death/killing of 1 animal meant nothing, but the extinction of a species meant a lot) Which was one of the most horrific things I'd ever heard, maybe because coming from an environmentalist, who are supposed to be the good guys. I guess it was the "animals only have value as things exploitable by humans" element to what she said, of which she seemed unaware. As if humans are the only life form with any value! Human, all too human.