Hi Eliz and thank you for the input.
In the end, we looked carefully at her ss and didn't do another test - we were exhausted and had to make a decision one way or the other fairly quickly. I'll explain my reasoning in case anyone is following who might find it useful:-
1. Rosa has never yet dropped low both early and late in a cycle. Although she does sometimes slide down late in a cycle, after she's gone low she's been in the clear by about 3 to 3 and a half hours later every time.
2. By that point, I was less concerned about her numbers overall as I was about the fact that she'd come up and slid back down. I was really looking for the slide to stop as she was still in the high green/low blue zone - I didn't think it was likely she'd slide back down into the lower greens, but I wanted to make sure her numbers were holding steady. I do understand the 3 rising number principle, but as her numbers recently often have little if any variation hour-on-hour, I don't always see 3 rising numbers in a row at any point in her cycle.
3. She had eaten some lc around +4.5 - not much, but enough on top of the hc that was only just clearing her system at that point. She also ate rather more lc at around +6.5 which, once she's in the higher greens after a low episode, is enough to raise her BG pretty consistently. She hadn't, however, eaten anything between +4.5 and +6.5.
This really came down to a 'know your cat' decision in the end. We did, however, leave her enough lc food for at least 3 cats in case she needed it and brought her to bed with us so we'd be very aware if she started getting restless and going to her food bowl repeatedly which is usually the only warning I get that she's dropping either quickly or lower than I'd like.