I wouldn't worry about her personality changing- there is absolutely no risk of that- it just means that she isn't going to be harassed by entire males and pups.
I don't think it is true that dogs have a tendency to get fat after neutering- only if you feed them too much. Entire/ un spayed dogs are naturally lean ( forget reason why?)
I wouldn't be to concerned about her recovery from the op- it is a very low risk one, she might be groggy for about 48 hours after the op but she will be back to her old self in no time. Females do take a little longer to recover than males in some cases but then, the op is totally different!
Hope all goes well- sure it will do

__________________