My aunt had performed pancha-samaskaram about 45 years ago from a head of a mutt in a village, but she does not remember any of the mantras. Can she perform pancha-samaskaram again by approaching another preceptor?

There are ways to remember the mantras. There is no need to perform Samashrayanam again.
The mantras will come back to memory by listening to Srimad Rahasya Trayasaaram kalakshepam and she can approach a preceptor for kalakshepam. It is accepted in tradition to emboss the conch and discus symbol again, but one should not perform Bharanyasam again. As per the laws of Brahmasthra which can be applied only once, performing of Bharanyasam again will not fructify at all.