Dogs dont really grow bigger after they are altered. They may get a little wider though. Like for example if you had major surgery, you might be a little sore and pack on a few along the way to recovery
That's the way I look at it. No real 'growth spurt' so to speak would occur as the result of a spay or neuter though.
Of course there are concerns about undergoing surgery, but I think the benefits far outweigh the "risks". You will reduce her risk of cancer of the reproductive organs to almost zero and that's one of the best benefits. Also, unaltered dogs are more territorial and unspayed females will have discharge all over when in heat. I have also heard that altered aids in preventing potty accidents, but I'm not sure about how true that is.
Best wishes for whatever you choose
