Yep I agree, she very well could be bi...
She could also be a lesbian who chose to have children. Lesbian and gay couples start families of their own too.
The book isn't out yet, and we have no idea how the author has portrayed her sexuality. But ultimately, Vasquez's sexuality isn't I thing I see any issues with, personally. I just don't think the scenario described in the synopsis, that Vasquez had children, jives with what we know about her as a character and her personality.
I am happy to see the author chosen is a hispanic female. That sort of representation does matter. I really just wish it was an all new character rather than someone related to a pre-existing character. There's been way too much of that already. It's stale, boring, and outlandish imo. I like to joke that if "alien" was supposed to be "jaws in space" then "alien: sea of sorrows" is "jaws: the revenge in space." Isolation was great, but pretty much everything related to Amanda ripley since then has been subpar. Other stories featuring Vasquez's family have already been done too. How many times are we going to see this family-relation angle pop up?