Gisela was angry (and also Gisela's husband) because Elisabeth's husband was protestant. Franz
Joseph was the one that supported them, but really he wasn't completely happy with this, I've read
that he said that he wouldn't imagine his grand grand children as simply counts or countesses.
In fact that this event damaged the relationship between mother and daughter, Elisabeth wasn't invited
to the celebration of the 50th anniversary of wedding her parents.