She’s not doing nose dives; she’s nadiring. With Levemir, you are going to see drops at onset and then through her nadir which comes later in the cycle. If she’s getting good duration, she can still be lower at preshot. She isn’t being unpredictable right now. She’s bouncing in between the lower numbers.
With Levemir cats, and she is not an exception, you should be on the lookout for her to onset at +3 (some onset at +4) and if she’s not bouncing, she will drop through the end of the cycle and her lowest numbers might be +6 - +9. As I mentioned, if she’s clearing a bounce or getting good duration, she might be low through preshot.