It is a risk, and if you can get her tested and then maybe PEP after that, but she would have to get tested now. As you should take PEP within 72 hours of exposure.
PEP is an VERY good idea. Please - if you can ask for Truvada + Isentress. These two are the standard treatment in US and UK. They are very well tolerated.
Do not give PEP recommendation, that is something to be discussed between the OP and his Dr.
Please do not wait on her HIV test results. The protocol is to start PEP immediately. Every hour you delay taking PEP reduces it's effectiveness.
The protocol is to start the patient on PEP and have the other person do HIV test. It's best that it be a PCR test but at a minimum it should be a 4th generation tests. This will insure that she is not in the process of seroconverting and negative by standard 2nd and 3rd generation tests including a rapid test.
Please do not wait. Do not delay. You can always stop later, but you can can't start soon enough!
PEP decision should be made by his Dr and him with no influence from this forum. PEP is not to be taken lightly and normally only used with people who had known risks.
His Dr (the clinic) has already offered him PEP.
This is a patient-to-patient support forum, and it's best advised to stay away from urging others to take prescription medication. That's a decision best handled between a licensed physician and the patient. Thank you.