For years now I've read people saying women could stay on an exogenous anabolic/androgenic cycle for very long periods of time (6+ months) and not suppress their endogenous production. Never made sense to me. After I did a cycle of topical DHT cream I certainly felt a bit of a crash postcycle. We still have the same checks and balances to our hormone production as men, only difference being the gland producing endogenous T (ovaries) and the amount produced.
Bottom line, I wouldn't recommend any different cycle length than you'd advise for a man, assuming she wants maximum retention of gains.