Even if the seller accepted your offer, that is one of many steps. That is the initial acceptance, but it's the lender who will make the FINAL decision.
A short sale doesn't mean a short period of time --- far from it. It may take more than 45 days to get a response from the seller who can accept, reject, or counter the offer(s).
Prior to the property being offered as a short sale, the seller and the listing agent should have already provided a lot of information to the lender that justifies the short sale. The lender could approve the short sale listing, or wait until after they receive an offer.
Regardless of how often the agent follows up with the lender, it is not going to expedite the process much, and may even a source of annoyance. One loan negotiator even has this greeting on his voice mail "Calls to follow up on status will not be returned as they only delay the process." Most negotiators may be handling 300 short sale files. If each agent calls each day, can you imagine fielding 300 calls a day?
Depending on the MLS rules and what the lender instructs the listing agent to do, the house could remain active on the market until after the lender --- NOT the seller --- officially accepts an offer. If another offer comes after yours, and it's deemed to be better than yours, the lender could accept that offer instead.
That's why when writing an offer on a short sale, give it your best shot. Submit your best and highest offer. A short sale doesn't automatically mean you should lowball an offer. Some short sale listings are very close to their true market value. This is where a realtor can help --- by providing guidance on comps, market conditions, and writing your offer.
Here's a very good article on How to Buy a Short Sale http://homebuying.about.com/od/buyingahome/bb/BuyingShortSale.htm.
You'll find links to other articles, but start with this one.