You have a large breed dog. They tend to grow pretty quickly. 58 lbs at 5 months sounds a bit heavy to me but if you can post a picture of her from the side and one from above we can better determine. Keep in mind some dogs grows faster than others. They dont all gain weight at the same pace. No, she's not putting on weight and growing for the winter.
Shasta GSD 5/5/10 CGC, ITD, TC
"Dax" Thor z vom Weberhaus BCAT CAX2 CGCA ETD HCT NCO-1 PKD-T RATI RATN RA TC TKA 3/18/2013
"Hades" Guilty vom Blutfeuer 10/26/2018
Zena GSD 6/1/03-2/16/2016
Riley GSD/BC 1/10/05-2/1/2013