What do you feed?
What do you consider "treats"?
Small amounts of anything (that is rabbit food) schould be no problem, and I've never heard about that 6 months. With 3 1/2 months she isn't very young anymore.
I feed greens, so pellets are a treat. They get some pieces for returning to their hutch, starting with 4 weeks. The sound of stirring the pellets in the plastic bowl sets them running for home after a few days.
Oatmeal is also fine. Or little, dried cubes of bread. Also pieces of apple, carrots, raisines, cherries, plums, dandelion etc. can be used as treats, depends on the preferences.
Just don't change their diet qickly, when introducing something new start very slowly, just morsels the first days, and increase the amount over 1-2 weeks so that the rabbit can grow the right bacteria to digest it.
You sure can buy expensive treats with lots of sugar, colours, artificial this and that in pet shops, but imho they are nothing better than bread or zwieback.
And don't overfeed the bun, they can get fat pretty quick, so be careful with treats rich in calories - they don't need that. Occasional a piece, but not handsfull distributed over the day, it sums up. Not just calories, but what they really need is lots of fiber in their food, grass, hay, etc. to keep their guts working and avoid serious problems.