The only PED I would imagine her using is something to help cut weight without losing muscle (Winstrol), like Cyborg did. The difference being Cyborg used steroids to gain muscle as well. Holm is a big woman and she's huge for the division. She might need something to help her make weight besides draining, especially after IVs were banned.
There's no proof until she fails a test though and I'm not saying she is taking PEDs.