Her anus looks very supple. I would not be surprised if some very long and thick things come out of her anus... a finger should not be any problem size-wise... but from her sounds she is not exactly happy being buggered by a finger... maybe she is embarrassed to have her anus penetrated...or afraid of what may be inserted there next! Having something in her anus at the same time does feel good on the penis, does it not?