Hi Patrice!
In my experience, most celebration "extra's" generally consist of confetti at a table, or a cupcake with candle for dessert. Different restaurants do different things, but on average, most restaurants that I've been haven't done the "Happy Birthday" song. However, when we visited Whispering Canyon Cafe' at Wilderness Lodge, they did sing happy birthday to a gentleman at the table right next to us (and they got the whole restaurant to sing along :-) So that being said, you may have better success at one of the "rowdier" restaurant experiences, such as Whispering Canyon or maybe even 50's Prime Time Cafe' at Hollywood Studios.
In any case, it's better that I type this than hear me sing: Tell your sister, "Haaaappy Birthdaay To Yoou!" for me, whichever day it falls on :-)
And good luck with all your Disney planning!