I have no knowledge of the spray but I've had the injection every year for the last 25 years and other than a sore arm I've only ever had a bad reaction to it once, and that was about 22 years ago! My point is, if you do get advised to go for the injection, I wouldn't worry about her having it too much. A lot of the people that talk of side effects blame it for giving them flu symptoms but it's a myth - it's just that it's given at the time of year when there are lots of colds about and it's coincidence.
Hope someone has some wise words on whether it's more effective or not for you