Hi Keri,
Have you tried The following?
At a neutral moment (i.e. not when she's crying or having a tantrum), sit her down (or have her stand up), and sit down in front of her so that your eyes are level, and looking at each other. Then tell her very seriously and earnestly, looking straight in her eyes, that you love her, and you love her no matter what she says or does, and you always will.
Then, preferably at another neutral time, ask her why she keeps asking you if you still love her when she's crying, and try to gently get the answer out of her - she may or may not be able to articulate it right then and there, but through questions you should be able to figure it out. Make it very clear that you're trying to understand, not blame, punish or justify. She may ask this because of the incident you mention, or it may be something else.. If you just assume it's because of this, you take the risk of missing the true cause, hence the opportunity to fix it quickly.
I did this with my son on a similar instance, and it worked wonders - by the way, the reason he was asking those weird questions had nothing to do with what I thought. It was because of an incident I hadn't even realized happened.
Hope this helps,
K.