unfortunately I don't have any wider information about pronouncation details of this word in english. still the way Your grandmother pronounced it makes me think she could be with origins in Europe - maybe french or german. by the way in german the fruit plum is pronounced [flam]. pretty close, isn't it? most probable Your grandma don't have any connection with Latvia. don't You know the maiden name of Your grandma? may be that could tell a lot of interesting things. from Latvia most of the immigrant to USA was just before the end of WW2. It was the time when our people was killed by russians and many of them was escaping to Germany and after that - to other countries, mostly - USA.