M.J.
First, I rarely hear of a thanksgiving bonus given to nannies, so she is a lucky one.
Second, 50 bucks is a LOT, esp considering she only comes twice a month! She she is lucky, again. Many full time childcare providers don't even get that much during xmas time.
Third, beware of this lady. If she is 'all about the money' then she may not be very into her job and thus, genuinely not really care for your children. Hopefully, she is not a slacker with them when you are not around.
Overall, people should be appreciative of whatever gift is given to them, even if it is a blessing. Those who expect too much (like this lady) out of life are never happy. Good luck.