I'm happy to have Ashley back in the squad as well. As long as they bring back Miranda in some capacity they will have done right in ME3.
Only if I can shoot her.
(I'm trying to decide whether I want to get her and Mordin killed in my import-for-ME3 run of ME2 I'm doing... though I suppose that might be harder now that both are loyal.)
You can definitely get a loyal Mordin killed, simply by sending him into the vent. A loyal Miranda on the other hand is surprisingly difficult to kill. I think you'd pretty much have to leave her to hold the line all on her lonesome, which would also require killing just about everyone else.
If you're desperate then you could always reload a save from before her loyalty mission, or just used the gibbed save editor to make her disloyal again...actually, have you done Jack's mission yet? If not, then all you need do is take Jack side in their little catfight and pick Miranda as a squadmate for the final boss.