Read and try. Pressing your tongue down to your jower jaw if you have to. It sounds really weird:
Certain consonants won't be affected at all, because they're all articulated by the lips: /m p b v f w/. The consonant /h/ is articulated only in the throat, so it will likewise be unaffected.
If part of her tongue remains in the back, and she can still use it, she might be able to retain (or approximate) consonants /g k ng/. These are articulated against the soft palate (velum) using the main body of the tongue, so a stump could still have reach. Same for a very throaty version of /r/.
With most of her tongue gone, I don't see any practical way to articulate /t d s z l y/ or a long string of other sounds that are made against the hard palate or teeth, but these could be approximated in some ways--for instance, hissing through the teeth, or replacement with a glottal stop