@shivles Could she have an upset tummy? Sometimes that can affect food absorption and lead to lows. Of course, that doesn't explain the highs, but perhaps that's overtreating the lows?
If she continues to stay lower than normal, you may want to speak to her DSN to see if her basal needs adjusting. If she's recently been diagnosed, then sometimes just starting on insulin can 'give her own islets a rest' and they then recover a bit and make some of their own insulin.
Other reasons could be a change of routine or stress or excitement. All you can do is monitor her closely, avoid overtreating hypos and overcorrecting highs, and possibly stick to 'safe' meals which you're confident would normally give good results for her.