I agree with what others said. It's likely she doesnt mean what she says, but is so emotional and scared right now that she is short with the ones who love her most. Instead of offering kind words that she might not want right now, offer to listen is she just wants to vent. She's not going to want advice, but rather compassion. Instead of telling her to be strong (which helps to be steong sometimes, but sometimes we need to be weak and cry and we don't want to be told to be strong, b/c it's really hard to be at times and if we're not, we feel like we're letting ppl down), after she vents --tell her something like "that sounds upsetting/scary/frustrating" etc., depending on what she says. Don't know you know how it feels, just let her know you hear her and that you're going to be here with her no matter what. Emotions can change daily.
Best wishes to you all.
P.s. Chemo is really tough--so, let her know she's entitled to her emotions! I finished in September , age 32