I also have a very active climber and she often played with the older kids when she was in her first year of school as most of her classmates didn't have the same interest or skill level with the climbing equipment and monkey bars

Personally I'd sit back and watch for a bit and continue to encourage play dates with similar aged friends as well as the older girl. Monitor it and if it seems her otheR friendships are suffering for it talk with the teachers

Dd's school is small so she knows all the students there which is nice but they have one day each week for reception to grade2 to pay on the big equipment and one day for the older classes so they do get their space and opportunity to play with their peers