I think she got too hot. Since the color change, she stopped growing as fast. http://img408.imageshack.us/img408/3541/0000027nc6.jpg
Could be heat stress as you say. But could possibly be a nutrient deficiency. If it is heat stress you should move your lamp away from the plant a little and make sure there is air circulating around the plant to prevent any static heat buid-up. Water as normal and she should re-start normal growth again soon. ;o)
Are the leaves folding together into a "V". If they are odds are it's a magnesium def. They call the leaf folding "praying for mag." I just finished dealing with one and it sucks. It can be fixed with epsom salt, but be very careful you don't overdo it with the epsom, too much salt in the soil and there will be no nute uptake.
