[@Sublimation]Hmmm... tweak the passive radius of her toxin so that it only affects people who are either breathing the same air as her or are stuck in a small, enclosed space with her and you should be good to go. Since she's not as good at shapeshifting as a normal slime, she can occupy an offense role due to something like cephalopodan "liquid muscle" (or so I'd imagine).

If I may make a suggestion, since this appears to be an expansion on or a subspecies of the shoggoth from Monster Girl Encyclopedia, why not just refer to her as such? xD