Girlfriend's Blood Sugar Dropped After Eating and Drinking?

So tonight was just any other night. My girlfriend and I ate our dinner and she took her insulin (humalog) for it. She's a type 1. Two hours later we tested her blood sugar and it was 145. She has a habit of going low while sleeping and I have had to pull her out of seizures twice now in our relationship. (One year) Because of that, she ate a rice cake which has 7g of carbs and drank a bit of gatorade. We figured this would raise it to just over 200. She corrects it when she takes it in the morning. Well, about an hour later, she's sleeping and I woke her up to test it just to make sure it went up. It went down to 87. Why would this happen? I just had her drink more gatorade and I'm going to have her check it again about 20 minutes, but I'm worried tonight will be another seizure night. Any ideas?