[Help] To spay or not to spay my new dog - 2 year old sheltie/daschund - that is the question.

Hi there! I recently "adopted" a 2 year old sheltie/daschund. I use quotation marks because I didn't get her from a shelter - I got her from my friend whose dad brought her to a shelter (without her knowledge or consent) and she got her back and asked me to take her in.She is completely house trained, the only trick she knows is the one I've taught her in the short time I've had her which is to sit. And even that she has a hard time with. She shakes A LOT around new people and she has grown very attached to me. If someone picks her up and I am in the room, she just quivers in their arms and stares at me. I give you this information so you have an idea of what she is like.On to the question, she was not spayed and she is a bit over two years old. I want the ability to take her to daycare and training classes but can't if she isn't spayed. I talked to the vet and they recommended the training since it might help bring her out of her shell and stop hiding under our bed/shaking uncontrollably. But I also read that spaying after a year can lead to behavioral issues and may change her personality for the worse. So I feel stuck which brings me to you folks. Any advice would be appreciated! Especially if any of you have spayed their older dog and if everything turned out alright with it. Thank you for your help! via /r/dogs http://ift.tt/2roUomj