There is no point worrying about it. Youngsters bounce back from surgery quickly so that is the upside of it.
Your shelter, well lots of shelters have government regulations that they cannot adopt a pet out that is not altered. And it makes sense. They are in the business of dealing with dogs that people are unable or unwilling to take care of. Making sure those dogs do not reproduce is important. Unfortunately, vouchers for spay/neuter, and requiring people to spay/neuter within so many months, don't work. People don't bother, and the shelters have to deal with their failures. So they've been burned.
There are some types of cancers for which your dog has an increased risk, and other types, of cancer that your dog will not get. Call it a wash, as you had no choice in the matter. It is far better that your puppy is with you in a home at this critical stage, than stuck in a shelter until she is 6 months or 18 months old when people prefer to alter.
Jenna, RN CGC & Babs, CD RA CGC HIC
Heidi, RA CGC
SG3 Odessa, SchH1, Kkl1, AD
Ninja, RN CGC & Milla, RN CGC
Joy, Star Puppy, RN CGC
Dolly CGC & Bear CGC