We don't know definitively if Hildegard and her nuns had access to instruments or used them in their music-making. There are some scant general references to instruments and harmonic simultaneities recorded in Hildegard's extant letters and treatises. In one of Hildegard's medical writings, she references the monochord, an ancient one stringed instrument that provided the foundation of medieval music theory. Other medieval instruments that existed during Hildegard's life include the vielle, harp, portative organ, drums, and drone instruments, mentioned by Mandryka, such as the symphonia or bagpipes. Hildegard refers to instruments in this passage from her writings:There's no reason to think that Ordo virtutum would have been performed like monophonic song as far as I know - rather than with instruments improvising. Here for example, with a drone and some bells
here a bit more elaborately
"And so the holy prophets, inspired by the spirits which they had received were called for this purpose: not only to compose songs and canticles (by which the hearts of the listeners could be inflamed) but also to construct various kinds of musical instruments to enhance these songs of praise with melodic strains. Thereby, both through the form and quality of the instruments, as well as through the meaning of the words which accompany them, those who hear might be taught, as we said above, about inward things, since they have been admonished and aroused by outward things[.] They accompanied their singing with instruments played with the flexing of the fingers, recalling in this way Adam, who was formed by God's finger, which is the holy spirit."
Hildegard often speaks in metaphor, and this passage in particular is part of an elaborate metaphor about the importance of music in the lives of Hildegard and her nuns. The passage doesn't imply the use of instruments in connection to her music or for use in a liturgical context; however, it does indicate that she had an understanding of musical instruments that went beyond Biblical scholarship, and that she envisioned them as part of the divine music of the universe as she experienced in her visions.