My mother inlaw, started drinking almond silk in place of milk, due to lactose intolerance. she needs calories, due to weight loss, now she is experiencing diarreah since starting it. could this be from the silk?

Could be...: But there are many causes of diarrhea. If the almond silk is the cause diarrhea should resolve within a few days of stopping it. Prove that almond silk is the cause of diarrhea by drinking it after diarrhea has resolved. If loose bowel movements return promptly you will have a pretty unambiguous answer. Why not drink lactose-free milk?

Almond silk: Yes. If she has multiple food allergies see the allergist asap.