While within Tibetan Buddhism male novice monastics can upgrade their vows into the full ordination of a gelong (tibetan, sanskrit: biskhu), following the Mulasarvastavadin lineage observing 253 vows, this type of ordination never reached Tibet for women.
In the 1960s, The 16th Gyalwa Karmapa approached The 14th Dalai Lama on the subject, finding strong support by His Holiness to fulfill nuns' aspirations. Succeedingly, the first nuns were sent to receive the vows within the Mahayana Buddhism, where the Dharmagupta lineage had been kept unbrokenly since the time of Buddha Shakyamuni with 348 vows to observe, mostly to Taiwan and Hongkong.
These days women practicing within any of the four schools of Tibetan Buddhism who wish to receive the completeness of vows according to the Vinaya (rules of comportment) nowadays still have to request it within the Mahayana Buddhism of China, Taiwan, Vietnam, and Korea.
It is all of ours' sincere wish and strive to enable future generations of nuns to request and receive full ordination within our own respective lineages of Tibetan Buddhism. Many renowned Buddhist masters from various lineages of all Yanas highly support these efforts, including The Dalai Lama and The 17th Gyalwang Karmapa.
At the end of the First International Congress on Buddhist Women's Role in the Sangha: Bhikshuni Vinaya and Ordination Lineages in Hamburg in 2007, H. H. Dalai Lama declared:
"[…] There are already nuns within the Tibetan tradition who have received the full Bhikshuni vow according to the Dharmagupta lineage and whom we recognize as fully ordained. One thing we could do is to translate the three primary monastic activities (Posadha, Varsa, Pravarana) from the Dharmagupta lineage into Tibetan and encourage the Tibetan Bhikshunis to do these practices as a Bhikshuni Sangha, immediately. […]" The Buddhist Bhikshu Tenzin Gyatso, The Dalai Lama (translation PYCL)