I don't know if you're aware of it, but Lantus does not lower blood sugar with meals. Lantus is a slow-acting insulin that is used to maintain blood sugar over a 24-hour period & it has no peak. The purpose of Lantus is to try to mimic a non diabetic's production of slow-acting insulin.
What she needs is a fast-acting insulin with meals - like Humalog, Humulin or Novolin to prevent blood sugar spikes that occur when eating - especially when eating carbohydrates, which we need to eat.
Example: Before bed last night, I tested my blood sugar as I usually have to do. It was 205 (for me, that's just about right for safe sleep) & took my usual 20 Units of Lantus. When I woke up this morning, I tested at 221. That's actually around the same because glucose meters typically have a 15% error rate. The Lantus prevented a big blood sugar spike while I was sleeping - like 300-400 which occurs without it. Diabetics learn they need Lantus by spending a few nights testing blood sugar every couple of hours when they would normally be sleeping & not eating - between midnight & 8am. If they note spikes, they learn that they need a slow-acting insulin.