Roses themselves were introduced to Egypt via the Greeks and Romans. The Goddess Aphrodite (or Venus) was born from the sea-foam and during her birth, a white rose was formed from the waves. This is why it is associated with the Goddess. When Aphrodite’s lover Adonis died, She cried and the white rose became red with his blood. And this is why red roses are associated with the Goddess.
Aset (Isis)’s worship became greatly linked to Aphrodite so much so that there was a syncretic deity Isis-Aphrodite within the Ptolemaic period. Aset as a mourning Goddess would also be associated with the red rose. There are also festivals associated with both Goddesses called Rhodophoria or Rosalia which are associated with offering roses to the Goddesses. (Here is my previous post on that: Rhodophoria/Rosalia Festival).
Sources
Forrest, M. Isidora. Offering to Isis: Knowing the Goddess Through Her Sacred Symbols. St. Paul: Llewellyn Publications, 2005. (Rose entry: page 258-259)
J. Gwyn Griffiths, Apuleius of Madaurus: The Isis-Book: (Metamorphoses, Book XI) (Brill, 1975), pp 39; 159–161.
Perpillou-Thomas, Francoise. Fêtes d’Egypte ptolémaïque et romaine, d’après la documentation papyrologique grecque. (Studia Hellenistica Series 31). Peeters Publishers, 1993.
Fiercely Bright One 