She may having vaginismus.
For that there are few basic options you can give a try.
1.Make her calm and reassure.
2. Support her.
3. good enough foreplay
4.enuogh lubrication
5.Can use vaginaldialators for gradual exposure (unfortunately this is not available in Sri Lanka and import also prohibited) so have to use alternative methods (if you know whatI mean)
6. Find the cause for her vaginismus and treat it.
So if you can't do above things properly, you have to consult a doctor and take his / her advice / treatment.
Most importantly don't make her anxious or feel alone, which may affect her condition in a detrimental way.