General synonyms:
* Timidly
* Hesitantly
* Diffidently
* Reluctantly
* Bashfully
* Coquettishly (for a playful shyness)
* Demurely
* Modestly
* Tentatively
* Uncertainly
More specific synonyms:
* With reserve: If the shyness is more about holding back or not being forthcoming.
* With embarrassment: If the shyness is linked to feeling awkward or uncomfortable.
* With self-consciousness: If the shyness stems from worrying about how others perceive them.
* With a blush: If the shyness manifests physically.
The best synonym will depend on the context of your sentence and the specific type of shyness you want to describe.