I think that depends on the details of the 403(b) plan. What your sis is looking for is called and "in-service distribution." This is not forbidden by the IRS, but it not allowed by all plans. Whether or not it is allowed should be described in the summary plan description (SPD), which is available from the custodian of the 403(b).
My wife and I both worked at a non-profit hospital and contributed to a 403B plan in the 1990s. At that time, our only choice of plans were administered by insurance companies, VALIC, Aetna, etc. However, once we left the hospital for other jobs, we found out that we had to wait 5 years (I believe it was Aetna) after we stopped contributing to be able to transfer the money to an IRA without a penalty.
If she is still working, the initial question of in-service transfer applies. Even if she has stopped contributing.Thx. Have to find out if she is still contributing