Just want to second the petdiabetes wiki info - really good stuff there.
I have seen rebound happen from a drop too low (below 50), too fast (250 points in 90 mins), or a great distance (500 to 150). So although a hypo is the expected cause, it can be from just the body perceiving a dangerous situation is happening because the trend, if not stopped, will result in a serious hypo.
It can be very subtle.
ETA: I looked at your SS. What insulin are you using? It could be rebound causing the higher PSs, especially the 400s right now if the insulin is still ok and she isn't getting higher carb food.
I see that when you had her on 1u, there really weren't any spot checks mid cycle to see how low she was going. On Feb 4th you had that really low PS, so I wonder is she was on the way up or down at that point. Often the first few lows, while safe as 49 is, can cause a little rebound "bounce" because they aren't used to the number, but then things settle out if you hold the dose. I still think that the 49 at PS was an indication that a dose reduction might have been a good idea right then. She may need a skinny 1u (something like .8u).
Going from 411 to 79 today may set her up for alittle bounce too. Can you get a before bed spot check in tonight and/or some spot checks over the weekend?