Its likely that if your SIL hasnt started visitation yet, she will very shortly...ask her to write down the name and phone number of the worker who is in charge of the case. Here, many children are placed through private agencies, so contacting "CPS" might not help much. Also, your SIL should be going to court soon if she has not already and she should be notified of those court dates, as well as being appointed a lawyer to represent her during those dates. Here, i believe they have to go to court within either 24 or 72 hours (cant remember which) of removal, and then again at another point shortly after removal and then i believe every ninety days (minimum) thereafter. If you find out when a court date is, if its not too much of a hardship, you could attend...that is how my foster son's half sister ended up with relatives, she was in a foster home for a few months, but the relatives showed up in court and as soon as the judge was made aware there were willing relatives she was moved to them within a couple of days (they've since returned her to foster care, grrr) ---i realize your situation is different due to the out of state thing. But it would be good for the judge to realize there are interested relatives sooner rather than later.
Also, you might start putting all contact in writing in addition to calling, as its harder to "put you off" in writing, i believe it has to go into the file. You could even start with a general letter to "Supervisor of Foster Care, DHS" and send to the address for DHS in her area, explain all details in your letter (including your niece's full name and DOB if you have it, and your SILs full name and DOB if you have it), usually the supervisors take more direct action than just a foster care worker. I think if the foster care worker hears "out of state" they might think "paperwork nightmare"....sometimes you have to keep going up the chain of command. I told my foster care worker for my foster son that i want his sister placed with me but i need to move to a bigger place, and she completely blew me off. I may have to go up the chain.
Just coming from a foster parent perspective, if the case was headed to adoption, i would want to know sooner rather than later if there was a viable relative interested in the child. Sometimes foster workers tell the foster parent one thing, and the relatives another. I know a mom online who worked for nearly a year to get her niece from another state, and yet the foster parents were only told at the last minute and were under the impression they would be adopting.
Do you have any other relatives who live closer to your SIL who might be an option for placement?