Sarah, because of the schedule changes it's probably best to stay with 1.25U now. You need to be able to find a dose which will allow you to do split dosing. That's probably not as high as 1.5U, as you just found out. The splits based on 1.5U total extended her duration a little too much.
It's very easy, especially in the beginning to jump the gun on dose increases. The longer-acting insulins can take even a week to reveal how well a particular dose is working. Most of us have had a tough time learning to sit on our hands and not change things around so much.
In your case that's especially so with dose changes you do make, because you not only need to make dose changes but also since you're still trying to find her best dose. Then you are occasionally changing the shot times as well, which we consider having similar effect to dose changes. Each change, whether it be in dose or shot schedule, effects the overall BGs over the course of several days in some cases. Or more immediate, as you witnessed with the 53 last night. That's another reason to go down to 1.25U and see how that works for this week in to next.
I don't think there's another split dose needed for a little while yet, right? It may even be a good idea the next time to base it on 1U instead of 1.25U, just to prevent what happened last night. Also, .5U is easier to measure. But let's see how she does on 1.25U till then.
Sound like a plan?