Depends on the name on the account. If the account is in *YOUR* name, the only employer discount that can be added is through *YOUR* company.
Easy way around that, though. If your fiancee is eligible for Sprint service, and can have as many lines as you need on her account, then call *2 (with your fiancee there with you, too) and tell them you want open a new account for her and do a transfer of liability. Your phone numbers, contracts, upgrade dates, etc will all move over with you, and they will be able to put her employer discount on the account then. No cost, just takes a little bit of time to set up (not endless hours or anything, but it's not a 2 minute fix, either). Just be warned that your first bill on her account will look weird (prorated charges for partial month, then full month in advance), but the last bill on your account should actually have a credit on it (since you pay a month in advance). If they can't transfer that credit into her account, ask them to send it to you in a check.