Is it normal for a woman to occasionally experience physical arousal or an orgasm while breastfeeding her child?

Absolutely normal. One of the reasons that some women love to breast feed.
Yes. Although uncommon, it has been documented that the stimulation a woman receives to the nipple/areola complex can be sexually arousing. As far as orgasm, that depends very much on the individual. There are not a significant number of women who achieve orgasm with breast stimulation alone. Most women require some degree of direct or indirect clitoral stimulation to reach orgasm.