To Spay or not to Spay timing

We have a 5 and a half old month female Aussie Shepeard. She's our first-ever dog. Knock on wood, she's been amazing. She learns things alarmingly fast, has had zero bathroom accidents in months, loves her crate, and is sleeping through the night. We've had her in puppy class training every week since she was 3 months old and now she has a break till after the holidays from the classes. We have her booked in for her spay the first week of January as she will be just past the 6-month mark. When we booked the spay the vet recommended to us we do it before her first heat as it's a much less risky surgery at that point with a quicker recovery and we should look to get it done around 6 months to make sure it's done before her first heat. Well, we were in for a 1 on 1 session with our trainer yesterday and the topic came up and she was dead set that we need to cancel the appt and wait until after the first heat. She said vets only want it done early because it's easier for them (ie quicker and therefore better for business). She said "the science says" she will have fewer issues with joints later in life and the hormones of the heat will be good for her. So the trainer is saying the vet wants it done early because it's easier for the them and the vet is saying she needs 10-14 days of recovery so we should cancel that training block as the classes would be too strenuous. The two people we look to for advice have totally opposite views and we just want to do do what is right for our puppy