My daughter took several rec classes a week when she was 3 and 4. Phased out by 5 into developmental only. She enjoyed gym a lot and we got good discounts on multiple classes per family.
I suppose it depends on your gym- ours it totally oversubscribed and has a huge wait list for rec classes so you can't do more than one.
Personally, I would maybe think about something complementary to her gymnastics, ballet, dance, yoga etc. There's plenty of time for multiple classes per week if and when they make team! In the long run, ballet or dance might well be more help to her gymnastics in future than another hour of rec gym.
DD took 2 rec classes a week from age 3 to age 6 when she joined pre-team- she loved gymnastics and once a week wasn't enough for her- she wanted more.
I knew nothing about gymnastics when my oldest started taking just before she turned 5. She LOVED it! She wanted to go more and more. I asked her coach about taking another class and she said she thought dd would do great in another class. We did not end up adding an additional class, but I did let her take some private lessons--actually a lot of private lessons. At the time, they weren't that much more than adding another rec class and dd loved the attention. I would look into adding a dance class if there is one available.